Shizuo is a tall young man often seen wearing his trademark bartender suit and blue sunglasses. As a child he had brown hair, though he later dyes his hair blond as suggested by Tom Tanaka in middle school. He is noted by several characters to be a good-looking guy who resembles the actor Yuuhei Hanejima, who is actually his little brother Kasuka Heiwajima.
Shizuo is introduced to the viewers in the first few episodes as a violent, no-nonsense tough guy, on equal footing with dangerous characters, such as Izaya Orihara and Simon Brezhnev. However, it is implied that most of the time, he is quiet and nondescript, simply following Tom around as his bodyguard. Shizuo apparently does not really like violence and has misgivings about his own strength; unfortunately, he has a very short temper and when angered, his body "acts on its own" and he fights with incredible strength. This restive nature is why Masaomi Kida warns Mikado Ryuugamine to stay away from him, along with Izaya and the Dollars, telling him to 'not hesitate to run from him' in the manga.
Despite the fact that Shizuo used his power very often, he was (and to some extent remains) worried about it. This is probably the result of events in his childhood where his strength caused others to fear him, alienated him from others at school, and even at times inadvertently hurt people he cared for. It is noted in the light novels that Shizuo seems to loathe both his strength and, by proxy, himself, despising both his short temper and inability to change his violent ways. As a boy growing up, it is mentioned that he simply endured the "eternal hell" that came with his power's toll upon his body as he felt it was simply a materialization of his own anger, and thus what he deserved. As noted in the light novels, Shizuo is extremely lonely, partially due to his own fear of hurting those he cares for accidentally and partially due to his strength pushing everyone away from him. It is revealed he had fallen for a woman in the past, but was unable to control his strength and ended up injuring her severely despite only trying to save her. His strength also gradually alienated everyone around him, leaving him isolated and fully aware of the fact that he could never be seen as a normal person and not something to be feared again. As he matured, Shizuo came to the realization that all he truly wanted was to be loved by someone, but because of his condition could not love anyone. He believed he may have been able to forgive himself had his power existed to protect something, but also knew fully well that no matter what he fought for the world would always label his efforts as "violence". Thus, when Shizuo states he hates violence, it is implied that what he truly means is that he hates himself, as due to his very nature he is the definition of violence.
It is not until his run-in with the Saika Army that he is able to accept himself the way he is, since they claim to "love" him because of his strength, the first time anyone has told them they love him at all. He was able to use his strength to its fullest without holding back and still be loved and praised for it, and this gave him the motivation to begin to accept his violent ways, even assisting with his self-control to a degree and allowing him to stop a punch he had already thrown at the last second. Outsiders believe that the "slasher" incidents ended when he went after Shizuo, while it is actually when Anri Sonohara defeats Haruna Niekawa, but Shizuo still beat up many of Saika's daughter blades and only stopped fighting when they did.
Despite his violent temper, and fierce attitude, Shizuo is shown to be kindhearted with a deep rooted sense of honor and cares deeply for those who are close to him, including Celty, Tom, Vorona, Akane and Kasuka; he is also shown to be protective of children, as with Akane Awakusu.
Shizuo's great strength is explained this way: Normally, the brain restricts one's power, shutting down muscles in response to pain in order to prevent serious injury; Shizuo doesn't have this limitation, and is capable of using his full strength. His power is described in the novels as the naturally unlimited form of human strength, and Shinra Kishitani likens it to the incredible "adrenaline power" that people rarely display in times of emergency. Although he was chronically injuring himself as a child, over time his body quickly strengthened itself and caught up. Now, as an adult, he is able to use his power without destroying his body.
Shizuo is also capable of often superhuman parkour moves gained from years of chasing Izaya Orihara, who is very good at running away from him. They share an intense mutual animosity, and Shizuo simply seeing Izaya on the street usually results in Shizuo hurling a trash can, vending machine, or other dangerous projectile at him, followed by Izaya fleeing and Shizuo giving chase while angrily yelling "Iiii-zaaa-yaaa!" after him.
Shizuo stated that he grew up within a perfectly normal family and suffered no significant traumas during his childhood. His superhuman strength first surfaced when he got mad at Kasuka for eating his cup of pudding. He managed to pick up the fridge but the strain was too much for him and he ended up in the hospital. As the years passed, Shizuo's body, after years of abuse, managed to build up enough strength to withstand Shizuo's outbursts and effectively give him unlimited strength with no negative consequences to his well-being.
Once Shizuo entered middle school, he quickly became friends with Tom Tanaka after saving him from some bullies. Tom gave Shizuo a lot of helpful advice on how to keep others from starting trouble with him such as bleaching his hair blond so that he would be easy to recognize and earn a reputation. It manages to work until Shizuo entered high school and encountered Izaya Orihara for the first time. Shizuo and Izaya hated each other almost instantly and have developed a fierce rivalry. Their battles would frequently cause thousands of dollars in collateral damage requiring the frequent intervention of the police, as well as fellow classmate Hajime Shishizaki who was one of the only ones capable of standing up to Shizuo's immense strength.
Around his second or third year of high school, Izaya became wanted for a crime and he framed Shizuo as being his accomplice. Shizuo, who was under 18 at that time, flung a vending machine at the cops who tried to arrest him. The policemen investigated more and Shizuo was cleared of all charges. However, this incident caused his hatred of Izaya to escalate.
During his third year of high school, he is approached by Kazane Kinomiya for info about Shinra. He incorrectly believed that Kazane had a crush on Shinra. They talk about Shinra until bullies looking to fight Shizuo showed up.
After graduating, Shizuo drifted from job to job constantly getting fired from each one due to his temper or because of Izaya's plotting. He was also approached by a talent scout and instead nearly beat him to death for annoying him. Kasuka intervened and the talent scout approached him instead. After that, Kasuka visited him and gave Shizuo the bartender uniforms that he wears so frequently and asked him to settle down a bit. However, thanks to Izaya, he also got fired from that job. Eventually, Shizuo found a job working for Tom's debt collectors agency as a bodyguard. However, Shizuo usually went overboard when shaking down a client which would usually end with the company having to pay for any collateral damage.
Dollars/Mika Harima Arc
Shizuo makes his first actual appearance after picking a fight with Izaya while he was meeting with Mikado, Anri and Masaomi. As the two of them stare each other down, they are interrupted by a group of gangsters, led by Hiroshi, who Izaya had humiliated a few minutes earlier. Shizuo makes short work of them but Izaya get's away in all the chaos. He throws a vending machine at Izaya, but Simon catches it and they end up fighting. Afterwards, he is seen conversing with Celty, wondering about what Izaya was doing in Ikebukuro in the first place, considering his main office is in Shinjuku.
A few days later, Celty and Shizuo are hanging out in a park when a mysterious girl, Mika Harima, runs by. Celty grabs her arm while Shizuo calmly tries to asks her a question. Suddenly, Seiji come in out of nowhere and stabs one of Shizuo's legs with a pen. The distraction gives Mika enough time to run away. Shizuo lets Celty go after the girl while he dealt with Seiji. Shizuo incapacitates Seiji easily, despite being stabbed multiple times with his pens and decides to go home afterwards, casually wondering how to patch up the wounds.
Later Shizuo is seen in the Dollars meeting with Simon. In the anime, after the crowd disperses, he sees Izaya and chases after him.
Shuuji Niekawa, an investigative reporter, starts to interview Shizuo but pisses him off after mentioning Kasuka. Shizuo punches Shuuji across the street. The incident in question causes Shizuo to reflect on his life which led up to his current state.
Later, Celty tells Shizuo about her encounter with the Slasher a few nights earlier. Shizuo is angered that someone tried to harm one of his friends and starts yelling about finding and killing the Slasher at any cost. Celty manages to calm him down enough for them to start gathering information before Celty senses the slasher nearby. The two ride in on Celty's motorcycle in time to assist Kyouhei's group in apprehending the attacker. Shizuo incapacitates the Slasher, revealed to be Shuuji Niekawa, with Saburo's car door. Suspecting Izaya to have some hand in this, he goes to Shinjuku to confront him directly.
Shizuo attempts to start a fight with Izaya, accusing him of causing the Slasher incidents although Izaya continues to deny any sort of involvement. As the two continue to argue, Celty rides in and tells Shizuo that the slasher is still active, and that there is more than one. Shizuo joins Celty as the two ride off to resolve the issue once and for all.
Later that night Shizuo and Celty go to a park where they were surrounded by the Saika army. Shizuo tells Celty to find the source of the Slasher while he fought off the current swarm. Celty gives him a special pair of gloves to protect Shizuo from getting cut. As Celty rides off, Shizuo continues to fight through the Saika possessed citizens, seemingly enjoying himself as he did so. Eventually, Celty manages to locate the original Saika and neutralizes it with the help of Anri. Shizuo notices as most of the townspeople return to normal and stops his attack.
Yellow Scarves Arc
Shizuo is shown recieving repeated messages about Anri being chased by Yellow scarves members throughout the City, becoming increasingly annoyed at the constant updates. Coincidentally, the Yellow scarves member and Anri run into Shizuo during the chase and Shizuo beats them up out of frustration. As Anri thanks him, he brushes her off and says he's turning off his phone as Celty arrives to assess the situation.
A few nights later, Shizuo is shot by Horada, who claims that it was Masaomi who ordered the hit. Shizuo eventually makes his way to Shinra's apartment to get patched up, all the while professing his desire to kill Masaomi for having him shot. Shizuo eventually learns the truth regarding the situation and attempts to stop Horada from escaping by slicing off the roof of his car with a street sign when he drove by. When the car keeps going, Shizuo then throws the sign and strikes the middle of the car, causing them to swerve out of control while Kinnosuke Kuzuhara arrests them for traffic violations.
Shizuo and Tom are eating a take-out dinner on a park bench while on their way to a bank to cash in some checks they had retrieved from their "clients" for the company they work for. Out of nowhere, Egor and Ruri (dressed as Hollywood) appear in front of them and start fighting each other, catching Shizuo in the middle. Egor grabs the metal briefcase carrying the checks out of Shizuo's hands to use it as a weapon but ends up smashing it to pieces sending the contents flying. Shizuo mistakes Egor's actions as attempted thievery, and in a rage, he pulls the park bench out of the ground. He swings it at the fighting pair, catching Egor across the face and destroying it, and knocking Ruri clear out of the park, where she flies lands in front of Kasuka's car.
Despite being the catalyst for many of the events in the arc, Shizuo is not seen again until the very end of the novel, after the motorcycle chase involving Celty and several other members of the Dollars. When a few members of the out-of-town Toramaru motorcycle gang who escaped the battle against Egor and Ruri at the underpass are riding away, they look to vent their humiliation and make themselves feel better while the police and local motorcycle gangs are occupied. They ask Tom and Shizuo about local gangs, and when Shizuo loses interest in the conversation and turns to walk away, they attack him, tearing the sleeve of his shirt. In a rage, Shizuo throws one man and his motorcycle at the others, sending the Toramaru thugs flying.
Later, he and Tom attend the hotpot party at Celty and Shinra's apartment, along with most of the main cast (minus Izaya and Masaomi).
Shizuo and Tom are having lunch at a cafe. They talk about the recent incident with Toramaru and Celty and mentions how Chikage Rokujou, their leader, is out for revenge. Shizuo remembers Chikage from the previous night, having been challenged by him personally. Tom asks how the fight went and Shizuo explains that, while he won (as expected), it took four punches from Shizuo for Chikage to finally go down. Then, Shizuo took Chikage to Shinra since he didn't want to just abandon Chikage in the street like that.
Tom also suggests that it's about time Shizuo got a girlfriend but Shizuo claims that there aren't any girls who would be interested in him. As if to spite him, Shizuo looked out the window to see a young girl with black hair staring at him with her face pressed against the glass. Shizuo goes out to see why the girl is staring at him only to get a stun gun to the stomach. After a few seconds Shizuo knocks the stun gun out of her hand, accidentally knocking the girl down in the process. Seeing that the situation is turning to their favor, Tom and Shizuo were forced to flee the scene to avoid getting the police involved. Much to Shizuo's dismay, the little girl is clinging to Shizuo's belt yelling for him to die. Not wanting to get their manager or Kasuka involved, Shizuo and Tom go to the only person they know who didn't matter if the cops showed up.
At Shinra's apartment, Shinra is appalled that Shizuo would knowingly kidnap a little girl, who says that her name is Akane. After Akane collapses due to a fever, Shizuo and Tom listen to Shinra's ramblings for several minutes about Celty before the girl finally wakes up. As Shinra questions her, Akane mentions Izaya and his address which causes a storm of rage to erupt within Shizuo. Much to everyone's surprise, however, Shizuo smiles and laughs kindheartedly at the whole thing. He tells Akane that he and Izaya are friends and that Izaya was probably using her for another one of his pranks. Tom commends Shizuo's acting after they leave the apartment. Shizuo asks that if he gets arrested for murder tomorrow, Tom tell their boss to act like Shizuo was fired yesterday.
Shizuo storms off to Izaya's apartment/office. Once he arrives, he sees a crudely written note saying that Izaya had moved with directions written on the back. Shizuo gets even angrier and runs off to the new building. When he opens the door, Shizuo notices something wrong. Within the dimly lit room, he sees three individuals in suits murdered in various ways. Their corpses seemed to suggest they were killed with bare hands much like how Shizuo would've done. Before Shizuo can leave, one of the members of the Awakusu sees him standing over the bodies and proceeds to run away and call his boss. Shizuo leaves the building immediately before he can come back.
Dollars and Blue Squares Arc
Shizuo is confronted by several members of the Awakusu over the deaths of their colleagues but, instead of fighting them, he runs away by climbing up the side of a building, displaying excellent skill at Parkour accumulated over years of chasing after Izaya. After Shizuo loses the Awakusu, he receives several messages from the Dollars website. He skims through them while thinking about how to clear his name when he sees several posts about Kyouhei and Chikage fighting near Raira Academy. Shizuo reads through with more attention and notices a post by "Nakura" suggesting they kidnap Chikage's girlfriend to make him stop. Shizuo decides that he should try to rescue the girls who were being targeted and goes to Raira to intercept the kidnappers. When he arrives at Raira, he sees a motorbike parked up front and picks it up, intending to use it on the rogue dollars members. He also spots Mikado on the side of the road, recognizing him from the Hotpot party several months ago. He also remembered that Mikado was part of the dollars and tells him that he is quitting as of today. Shizuo states that it's because he didn't want to be a part of a group that was low enough to kidnap students.
Shizuo then moves on to deal with the kidnappers. By this time, the fight has escalated into a battle between the rogue Dollars members against Kyouhei and his gang (plus Chikage). When Shizuo arrives, Anri, and Vorona have also gotten caught in the crossfire. Shizuo asks whose motorbike he's carrying and Vorona answers that it's hers. Shizuo puts the bike down now that he knows who the owner is and proceeds to beat up the remaining kidnappers who haven't been incapacitated yet, sending each of them flying. Unable to contain herself any longer, Vorona throws her knife into Shizuo's chest which causes Shizuo to have a flashback to one of his and Izaya's chases, and sends him into a rage.
Shizuo then proceeds to chase Vorona all across Raira after declaring that he doesn't like hitting women, but she'd better be ready to have her expensive looking helmet crushed between his hands until she gets in the back of her getaway truck. Shizuo catches up with her and spots Akane tied up in the very back of the cargo compartment. Before Shizuo can reach for her, Vorona attempts to shoot him with her rifle which forces him to retreat. As Shizuo watches Slon and Vorona drive away with Akane, he looks around for something he can use and spots an abandoned car off to the side. Shizuo kicks the car around like a soccer ball and knocks it towards Vorona who blows it away with her rifle.
Shizuo uses the distraction to climb on top of a fence which he uses to leap on the the side of a nearby apartment building. Shizuo runs along the side of the building until he catches up with Vorona and Slon and jumps, bashing through the roof of the truck and landing between Akane and Vorona. Vorona, with regret, attempts to shoot Shizuo in the head but is stopped by Celty. A sudden jerk by Slon causes a crate full of combat knives to fall and Shizuo shields Akane with his body.
Once he made sure she was unhurt, Shizuo slams his fist into the floor of the truck, effectively breaking the cargo compartment in half. Shizuo takes Akane and leaps off the still moving truck while Celty's shadow moves to cushion their fall. Slon and Vorona retreat for the time being and Celty goes to make sure Shizuo is alright. Akane asks why Shizuo saved her despite the fact that she's trying to kill him. Shizuo simply replies that he's glad that she's safe and smiles. Akane smiles back at Shizuo warmly.
Izaya in the hospital/Namie vs. Mika Arc
After Vorona joins up with Shizuo and Tom's debt collection agency, she is assigned as Tom's second bodyguard. While they take a break in the hallway, Shizuo asks Vorona if he has seen her before (she was wearing a biker's helmet when they fought). Vorona asks that she refrain from answering until a later date as she doesn't know how Shizuo will react if he finds out she's the one who he fought with several weeks ago. Shizuo responds by giving Vorona a can of coffee and saying he's glad that he finally has someone who will call him senpai for a change.
Kasuka arrives at Shizuo's apartment asking for his help. Shizuo is a bit surprised by the sudden visit and assumes it is because he and Ruri are getting married. Kasuka denies that and says that it is about Ruri's stalker. He tells Shizuo that he needs someone to take care of his cat and leaves Yuigadokusonmaru in Shizuo's care. Shizuo brings the cat to Shinra's house. When he walks in Shinra was laughing really loud so Shizuo kicked him across the room.
With Shizuo was Ruri and Kasuka. Shizuo told them that he is letting them take care of the cat because they understand the Dollars. Everyone present converses.
Later, Masaomi Kida returns to Ikebukuro and approaches Shizuo. Masaomi apologizes to Shizuo about him getting shot by the Yellow Scarves over a year earlier saying that even though he did not order it, he still has to take responsibility. Shizuo accepts Kida's apology but pokes him in the head (which is about as strong as a punch) for not addressing him with respect, knocking Kida out.
Dragon Zombie Arc
Shizuo is asked about his relationship to Izaya by several delinquents who want to get back at Izaya for scamming their boss. Shizuo offers a bit of insight into his and Izaya's life in high school saying that he was never able to lay a finger on him. The only person who could ever catch up with Izaya was someone he referred to as "Shishizaki-senpai." He also states that when he finally does kill Izaya, he will make sure not to involve Tom, Vorona, or anyone else if he gets arrested for it.
Kadota's Coma Arc
Shizuo is arrested under false charges according to Izaya's plan (as it turns out Izaya is not the only one who wants Shizuo out of the way for the upcoming event). Shizuo willingly leaves with the police since he believes the charge is a misunderstanding and it would eventually clear up. He is interrogated by two police officers and finds it odd that they are not interested in investigating the charges at all; instead, they spend the whole time purposely trying to make him angry (even going as far as threatening to plant illegal drugs in Kasuka's house and arrest Kasuka). Shizuo is alarmed when he notices the officers have red eyes.
The officers admit they are Saika's children (with "a different mother though") and their mission is to create an excuse (ex. getting Shizuo to assault a police officer) so they can remove Shizuo from the streets of Ikebukuro. Upon realizing that he is dealing with Saika instead of regular human beings, Shizuo is ready to let his anger take over and just beat them up when Kinnosuke Kuzuhara kicks open the door. Kuzuhara was outside of the room and heard the officers threatening Shizuo. He warns the officers to better not try anything funny because Kuzuhara has "connections" within the police force and he will report their misconducts. After Kuzuhara leaves, Shizuo calms down and notes that his opponent this time is not Saika's children but his own temper. He resolves to control his anger and waits for his boss to bail him out the next day.
Shizuo is still held in the police station.
Saving Izaya/Haruna returns Arc
Shizuo only appears in the very end of the volume. The guy in the cell next to Shizuo's was under Saika's influence. He asks Shizuo to make a scene so that he can take Celty’s head from the police department (since it was brought there for an examination). While Shizuo was considering the offer, the police come and releases him from the jail. While he walks out of the station, there's an explosion next to the police car.
Someone by the car leaves with a box. Shizuo isn’t sure what happened but he suspects it’s Vorona and that the box contains Celty’s head. He also thinks that Izaya is behind all this somehow and that there's a reason if he was released from prison so suddenly. At this point he's pretty pissed off.
Shizuo witnesses Celty's rampage through the city, wondering what caused her to act this way. Suddenly, Shooter, Celty's horse, rides next to him, signalling him to jump on so that they can confront the person responsible for Celty's current state. Shizuo agrees but asks Shooter to transform into a regular bicycle as he doesn't have a motorcycle license. Shooter takes Shizuo across the city, unaware that Izaya was tracking them as well, to an old warehouse where they find Kasane Kujiragi and Vorona hiding out. Shizuo confronts Kujiragi over Celty's berserk state but Vorona steps between them and points a gun at Shizuo. Shizuo tells Vorona to get out of the way but Vorona remains steadfast in defending her current client. As the situation grows more tense, Vorona suddenly lunges at Shizuo, startling him, as she knocks him to the ground. As she does so, a large number of Steel beams crash through the roof of the warehouse, embedding themselves in the concrete floor. Vorona is also hit by a stray metal pipe which significantly wounds her. Kujiragi escapes while Shizuo attempts to tend to Vorona's wound.
Shizuo scolds Vorona for trying to protect him and doing something so reckless, but Vorona insists that her injury isn't very serious. Vorona then calls Shizuo's attention to Izaya who was observing them from a nearby building. The crane that held up the metal beams started to fall, but Shizuo simply punched it out of the air and towards Izaya. The crane didn't reach it's intended target, but it was clear what Shizuo was thinking at this time. Before Shizuo can act, Izaya calls him on his Cellphone. Izaya taunts Shizuo, teasing him about his inability to protect his friends and accuses him of having feelings for Vorona and even Akane. Shizuo notices Izaya standing on top of a nearby building, gazing down at him. Shizuo calmly tells Izaya "Goodbye." before hanging up. After confirming Vorona was alright, he smiles at her briefly before turning to leave. Shizuo tells her to be careful around him as he can't think rationally at this point, even giving her permission to shoot him should he go out of control. He then leaves to fight Izaya one last time, ignoring Vorona's attempts to calm him down.
Final Curtain Arc
Shizuo reaches the building Izaya is waiting in and is greeted by a burst of flame springing forth from gasoline that had preemptively been spread across the floor. Shizuo rips the door he had just entered from off its hinges and uses it to smother the fire before it is able to spread. Izaya has several more minor traps lying in wait for him, but these are ultimately to distract him from the carbon monoxide leaking its way around Shizuo. Robbed of his breath, Shizuo is brought to his knees as Izaya once again sets fire to his surroundings. However, Celty extinguishes the fire from above with her shadows, and Shizuo punches his way through the flooring below. Izaya loses track of Shizuo until he rips the scaffolding Izaya is standing on out from underneath him. Shizuo hits Izaya with the steel beam he tears away and sends Izaya crashing through a nearby building.
Izaya runs away until they reach the crowded Tokyu Hands where he finally turns and faces Shizuo directly. Izaya manages to dodge Shizuo’s attacks and slashes at him repeatedly until a nearby stun grenade directed at the Saika army robs Izaya of his focus. This opening allows Shizuo to finally land a hit on him, dislocating Izaya's shoulder and breaking both of his arms upon a second blow.
Izaya accepts that he can’t win by force and resigns himself to his death at Shizuo's hands, reasoning that even if he is killed, Shizuo will be seen as a monster and be put to death for murder. Shizuo goes to land the final blow, but Vorona intervenes and stabs Izaya. Vorona asserts that Shizuo is definitely human and refuses to let Shizuo stoop to her own level as a murderer, resolving to kill Izaya herself. Shizuo comes to his senses and attempts to stop Vorona, but before he is able to Simon notices the fight and throws a stun grenade at them. Vorona passes out as a result of the shock and the exhaustion from her own wounds, and Kine and Manami haul Izaya off in the confusion.
Simon, Denis, and Tom attend to Vorona, and Shizuo is grateful that she stopped him from becoming a murderer, but upset that she attempted to commit the very same act in his place. Shizuo then spots Shinra heading to the nearby building that Mikado and Celty are on and follows him to the roof. Once there, Shinra asks Shizuo to send him flying towards Celty, as per a previous threat that Shizuo would do so if Shinra ever attempted anything villainous towards her. Shizuo complies and flings Shinra as hard as he can through the air towards Celty’s retreating form.
With rumors spreading that Celty is the culprit behind Ikebukuro's recent kidnapping cases, Shizuo grows angry that his friend is being falsely accused of being a criminal. When he overhears Kuon mentioning his role in spreading the rumors, Shizuo grabs the boy and questions him, but Kuon deliberately enrages him further. Shizuo punches Kuon, knocking him into the air, but Kuon manages to avoid excessive harm by blocking at the last second. Seeing that Kuon is mostly unhurt after he lands, Shizuo makes to attack him further only for Yahiro to provoke Shizuo on Kuon's behalf. While Shizuo ultimately wins their fight in the end, Yahiro is able to hold his own shockingly well, managing to knock Shizuo down multiple times and leaving him with minor injuries.
Later on, Celty questions Shizuo about his fight with Yahiro. Believing Yahiro and Kuon to resemble himself and Izaya respectively, Shizuo expresses concern over the two boys' friendship as he believes Kuon will try and take advantage of Yahiro. Shizuo reflects on his relationship with Izaya and wonders how much trouble it would have saved the city had they managed to get along, but Celty retorts that it would still have been disastrous since Izaya would likely have tried to use Shizuo for his own shifty purposes. Shizuo agrees and asks Celty to keep an eye on Yahiro.
After Tom was attacked by the Slugger, he becomes determined to find the attacker. He is angered to learn that Kuon is responsible for Tom getting attacked and attempted to hurt the boy again before Tom punched Kuon instead.
A Sunset with Izaya Orihara
The introduced chapters in the novel are mostly interviews with other characters in the series, such as Shinra, Shiki, Kadota and Shizuo, regarding Izaya. Each of them realizes that the fact that they're asked about Izaya means that he must be alive. Shizuo initially refuses to participate, but then finally gives up. He says that Izaya has the tendency to become obsessive in a terrifying way once he wants something; to the point of risking his own life, which makes him think that their conflict may not end until somebody dies. He tells the person interviewing him to pass down a message to Izaya: to stay out of Ikebukuro.
A Standing Ovation with Izaya Orihara
A few months later, Shizuo is seen in Fukuoka City playing baseball with the cast of Hakata Tonkotsu Ramens. It is said he came all the way to Kyushu for a job and the members asked him to fill in for someone since he was around, although there is not much more known about the specifics of the trip.
- Main article: Kasuka Heiwajima
As children, Shizuo was very close to Kasuka due to the fact that Kasuka was one of the few people who wasn't terrified of Shizuo's monstrous strength. Even after Kasuka went into showbiz, he still took the time to help his brother find a job he could keep. He gave Shizuo several bartender uniforms after Shizuo found a job that didn't constantly send him over the edge. Shizuo promised to keep the job he had, but that quickly ended when Izaya framed Shizuo for an as-of-yet unidentified crime (in the light novels, he was fired for assaulting his manager). This event caused the two to grow rather distant. Despite this, Shizuo shows to be very protective when it comes to Kasuka such as how he maltreated debtor for trying to blackmailing Shizuo by endangering his brother's career.
As shown in volume 9, Shizuo seems to consider himself inferior to his brother. When Mairu called him "a nice guy like Kasuka," Shizuo told her not to insult his brother by comparing Kasuka to him. Likewise, Kasuka claims that his expressionless personality is primarily influenced by Shizuo. Due to the fact that Shizuo always lashed out at him the second he became even a little bit angry, Kasuka tried to balance it out by being the level headed one of the two. Kasuka even takes partial responsibility for Shizuo's rampages, such as when Kasuka finds out that it was his brother who knocked Ruri Hijiribe halfway across the city (not that he was even surprised).
- Main article: Shizuo and Izaya
Shizuo and Izaya easily have one of, if not the most negative relationship in the series. The two have hated each other from the moment Shinra introduced them. During their very first meeting, Shizuo threw a punch at Izaya after being antagonized; which prompted Izaya to slash Shizuo with his knife. Further into their fight, Izaya arranged for Shizuo to be hit by a truck.
Their fights have become legendary throughout Ikebukuro and have caused massive damage around the town.
Mairu and Kururi Orihara
- Main article: Mairu Orihara
- Main article: Kururi Orihara
Unlike their older brother, Shizuo is on friendly terms with the Orihara twins. This is most likely due to the mutual indifference they share toward Izaya. The twins even frequently cheer Shizuo on whenever they witness one of his and Izaya's trademark chase sequences. They often pester him to introduce them to his younger brother Kasuka Heiwajima, as they are huge fans of his acting.
- Main article: Tom Tanaka
Shizuo and Tom have been friends since middle school. Ever since Tom witnessed Shizuo in action, he tried to get on his good side to avoid getting killed. It was Tom who suggested that Shizuo bleach his hair blond so as to build up a reputation to keep the gangs away. After Shizuo was fired from his bartending job, Tom gave him a new job in the form of his bodyguard and the two have been partners ever since. Tom is also one of the few people who can calm Shizuo down after one of his rampages.
- Main article: Shizuo and Vorona
- Main article: Akane Awakusu
Due to Izaya, Akane wanted to kill Shizuo at first since she believed him to be an assassin after her father and grandfather. Shizuo was initially annoyed at Akane but the two grew closer after Shizuo saved her from Vorona and Slon. Because of this, Akane's feelings toward Shizuo are mixed. While she believes that Shizuo isn't after her family anymore, she still thinks he's an assassin and is too dangerous to be left unchecked (No one has told her otherwise or even knew she thought that in the first place.) With this in mind, Akane decides that the easiest solution is to become stronger than Shizuo is. She starts training at the same dojo as Mairu and Kururi.
- Main article: Celty Sturluson
Shizuo and Celty have remained on friendly terms for several years. They would often talk to each other about the problems they have and the events that surround them. Celty notes that she is one of the few people who never annoy Shizuo, most likely because she doesn't talk. He also talked to her about his childhood and how his monstrous strength hurt himself and other people. Shizuo, on his part, already knows that Celty is the Headless Rider but couldn't care less. He considers her a good friend and gets angry on her behalf, which is rare for him to do for others. Shizuo even went so far as to swear vengeance on the Slasher when Celty informed him of her attack.
In Durarara!! SH Novel, Shizuo nearly killed a Raira Academy Freshman who provoked him by claiming that the Headless Rider is the kidnapper and a monster.
In the Durarara!! 3way Standoff manga, Yoshimune asks if Shizuo has crush on Celty because of how much they get along, but he didn't understand the question and didn't answer.
- Main article: Shinra Kishitani
In volume 05, Shizuo states that Shinra is a "Bad acquaintance that stuck." Shinra considers Shizuo a friend, but the feeling isn't entirely mutual. Still, the two remain on mostly good terms with one another although Shizuo is sometimes annoyed at Shinra's ramblings.
- Main article: Kyouhei Kadota
In volume 10, when Shizuo learns that Kyouhei has been injured in a hit-and-run, he angrily yells that he won't forgive the bastard that hurt his old acquaintance. Shinra describes Shizuo and Kyouhei as two of the most influential members in Dollars, even after Shizuo has left Dollars. Be it an external threat or an internal conflict, Shizuo serves as a deterrent in terms of physical force (anyone who wants to start a fight in Ikebukuro will be neutralized by Shizuo) while Kyouhei serves as a deterrent in terms of leadership (members tend to unite and follow Kyouhei since he is a decisive and reliable leader).
- His name is ironic. Heiwa (平和) means "Peace/Harmony" while Jima (島) means "Island," leading his last name to translate to "Peaceful Island." Shizu (静) means "Quiet" and "O" (雄) means "Hero/Masculine/Leader," leading his first name to translate to "Quiet Hero."
- His hobby is basking in the sun.
- Shizuo likes all dairy products and sweet things, but dislikes beer and anything bitter.
- While he may not be a decent cook, Shizuo can at least make curry for himself. Although, Ryohgo Narita claims that he generally makes cup noodles.
- One of his favorite and oft-repeated quotes is "I hate violence."
- He hates switchblades because Izaya uses them.
- Shizuo mentioned that he wanted to be a detective when he was a kid.
- He smokes Blue American Spirit cigarettes.
- According to Tom, the reasons Shizuo has never been arrested for all the destruction he causes during his rampages are: 1.) the people he beats up are usually the ones who can't or won't go to the police (ex. gangsters); 2.) his boss has been paying for the damages; and 3.) the destruction he causes is too ridiculous and humanly impossible (in other words, a judge probably will have a hard time believing that a young man has ripped a light pole up from the ground and bent it in half with his bare hands).
- In the second light novel, Celty claims that Shizuo has yet to kill anyone.
- Also in the second light novel, Shinra explains how it is possible for Shizuo to have the strength he possess without having huge muscles.
- Originally, Shizuo was the one approached by a talent scout, not Kasuka. Shizuo, annoyed by the scout, nearly beat him to death. Kasuka rescued him, and the talent scout decided that Kasuka was just as good and scouted him instead.
- He sang Tsugaru Kaikyou ・Fuyu Geshiki in the rapping CD.
- Shizuo's birthday is January 28 while his voice actor Ono Daisuke's birthday is May 4. However, Izaya Orihara's birthday is on May 4 while his voice actor Hiroshi Kamiya's birthday is on January 28.
- The two voice actors, Kamiya and Daisuke, are best friends in real life.
- In the original script, Shizuo was not going to be in the story. However, Narita didn't want Izaya to be "this unstandable, unbeatable overpowered antagonist," so he came up with someone who would be his counter to stop him, and thus, Shizuo was created.
- Shizuo Heiwajima, Celty Sturluson, and Izaya Orihara appear as DLC demons for Devil Survivor 2: Break Record.
- Shizuo is a playable character in Dengeki Bunko Fighting Climax. In his in-game story, he is dragged into the alternate world's story by an entity named Denshin, who wishes for Shizuo's help to defeat the malevolent being Zetsumu (who has absorbed the universes of all of the other characters, giving him godlike power). Shizuo faces Zetsumu in a long battle and defeats the villain, destroying its physical existence and bringing peace once more. Denshin then sends Shizuo back to his own universe after all of the others are restored.
- Shizuo plays with the Hakata Tonkotsu Ramens grass-lot baseball team, filling in for one of their teammates. He hits home-runs out of the baseball field and eventually breaks someone’s car windshield with one of these home-runs.
- In Durarara!! SH, Shizuo said that when he was a kid he wanted to be a detective.