Shizuo Heiwajima/Relationships

To be reworked.

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).

Izaya Orihara
Shizuo and Izaya 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 constant battles have become common place in Ikebukuro to the point that even the police have long since given up trying to apprehend Shizuo for the destruction he causes simply because it happens so often.

The two of them are almost complete opposites of each other both physically and mentally. While Izaya is a calm and mostly collected individual who remains emotionally detached from most situations, Shizuo reacts impulsively on almost every single turn, causing him to go on a blind rampage. Where Izaya tends to use his superior agility and precise planning to get what he wants, Shizuo almost exclusively uses brute force to achieve his goals. While both methods have proven to be effective, Shizuo tends to leave a lot more destruction in his wake that causes problems for him in the long run.

Izaya and Shizuo are also different in their maturity. Shizuo is prone to random outbursts and sudden rages, and has little self-control. He is known to become angry very easily and as a result is feared because of this. However, he ultimately has a very mature goal to live a peaceful life and become strong enough to control himself. Unlike Shizuo, Izaya presents himself with a professional attitude when dealing with clients, and keeps his cool even while being tortured. In contrast to this, he is highly impulsive and unethical, often acting on a whim.

While Shizuo frequently expresses a strong desire to murder Izaya in the most painful way possible, he is in fact the less aggressive of the two of them. This is pointed out by Shizuo himself in the ninth light novel, where he explains that while killing Izaya would be satisfying, he would be perfectly content if Izaya simply stayed out of his life completely. In their fights, Izaya is usually the first to act; when Shizuo is the one to attack first, it is usually because he believes that Izaya has provoked him in some way or his actions are harming others and he needs to be stopped.

Mairu and 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.

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.

Vorona
Although he was unaware of it at the time, Shizuo and Vorona first met during the battle at the Raira practice fields. Shizuo quickly gained Vorona's attention due to his inhuman strength and ferocity. Even though she technically failed her mission, she expressed nothing but excitement and joy at the prospect of fighting Shizuo again which becomes one of her primary motivations throughout the series.

Shizuo formally meets Vorona shortly after his boss hires her at Simon's recommendation. Shizuo's boss assigns Vorona to work under Shizuo, the official reason being that Shizuo is supposed to act as her mentor and show her the ropes (a task he accepts with much enthusiasm). The real reason, however, is so that Vorona can act as a deterrent towards Shizuo's tendency to cause untold amounts of collateral damage when angered. Basically, Vorona acts as the muscle when Tom begins to shakedown a client unless said client proves to be especially resilient. In which case, Shizuo is called in to take care of it.

Shizuo appears extremely excited about having a junior colleague to work under him due to the fact that Shizuo normally gets fired before he can gain any sort of seniority wherever he works. Shizuo takes his role as mentor very seriously and treats Vorona like a protege through most of their initial interactions. As the series progresses, Shizuo begins to regard Vorona as not just his junior but also as a close friend in the same way as Tom or Celty.

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.

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'', 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 doesn't understand the question and doesn't answer.

Shinra Kishitani
In the fifth light novel, Shizuo states that Shinra is a "bad acquaintance that stuck." Shinra considers Shizuo a friend, but the feeling isn't entirely mutual. The two remain on mostly good terms with one another, although Shizuo is sometimes annoyed by Shinra's ramblings.

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).