Mika Harima Arc

ARC undefinedThe Dollars/Mika Harima Arc is the first arc of the Durarara!! series. It focuses on Mikado Ryuugamine's first days in Ikebukuro, Mika Harima's disappearance, and the Dollars.

Plot
The arc begins with Mikado Ryuugamine's arrival in Ikebukuro after accepting an invitation from his childhood friend Masaomi Kida to attend high school at Raira Academy. During Mikado's first tour around the city, the pair encounter Masaomi's acquaintances Walker Yumasaki and Erika Karisawa, carrying bulging backpacks of manga, and Simon Brezhnev, who invites them to eat at his restaurant, Russia Sushi. As they walk on, Masaomi warns Mikado of people in the city he should never mess with: Simon, Shizuo Heiwajima, and Izaya Orihara. The pair hear a sound like a horse neighing, and Masaomi begins running to an intersection nearby, where they witness the legendary Black Rider driving by on a pitch-black motorcycle.

In an online chat room, TarouTanaka tells other members that he is moving to Ikebukuro. They congratulate him, and Kanra shifts the conversation to the urban legend, the Black Rider. It is said that the Rider rides a black, plateless motorcycle that sounds like a horse, and underneath its helmet, it has no head.

Elsewhere, a group of men wait for their boss in a parking garage. The Black Rider appears and fights the thugs to reach their van. One manages to knock off the Rider's helmet to reveal neck with no head attached.

After securing the safety of the trafficking victim in the thugs' van, the Black Rider returns home. She is greeted by Shinra Kishitani, who hypothesizes on her ability to see and hear without a head, a result of her being a Dullahan.

The next day is Mikado and Masaomi's high school entrance ceremony. In class, the seat behind him is empty and the girl who sits there, Mika Harima, is absent.

On their second day of high school, Mikado and Anri Sonohara volunteer to be class representatives. Later that day, as Mikado and Masaomi are wandering the town, they spot Anri being harasses by a trio of bullies. As Mikado approaches to help, Izaya Orihara pushes him from behind. Izaya scares the bullies off, and Masaomi introduces him to Mikado. A man in a bartender uniform yells Izaya's name, and Izaya excuses himself and runs away.

Elsewhere, in a van, Shimada is beating one of the kidnappers in the back of a van, but the man refuses to reveal who he works for. Shimada lets Walker and Erika take over, but Kyouhei arrives in time to stop them and lets the thug go. Now aware that the company Yagiri Pharmaceuticals is hiring thugs to kidnap illegal immigrants as test subjects, they watch the building from the outside. In her office within Yagiri Pharmaceuticals, Namie Yagiri sends her subordinates after a missing subject.

In town, Celty and Shizuo Heiwajima spot Seiji Yagiri and a girl with a scar on her neck. Celty recognizes the face of her missing head on the girl and grabs her. When Shizuo tries to calm her down, Seiji stabs him with a pen. The girl screams and runs, and Shizuo throws Seiji across the street.

The running girl bumps into Mikado Ryuugamine, and seeing her pursuer, pulls her into the subway. She appears to have amnesia and refuses to go to the police, so he allows her to stay with him that night. The next day, Izaya Orihara and the Black Rider follow Mikado home from school. He tells Celty everything, and she asks to speak with the girl, but when they arrive at his apartment, the girl is gone.

Putting the string of events together, Mikado opens his laptop to the Dollars homepage as Celty and Izaya watch with interest. Shortly after, Namie Yagiri receives a call from Mikado asking to make a trade.

That night, in central Ikebukuro, Celty waits on a rooftop. Kyouhei and his gang bring the girl with the scarred neck up to meet her. On the street below, Namie and her subordinates, dispersed throughout the thick crowd, spy Mikado, alone. Mikado offers her the location of the girl in exchange for her company turning themselves in for their illegal human experimentation. Namie dismisses him and signals his men as Mikado sends an email.

Mikado, the leader of the Dollars, reveals himself by sending a mass email to all members, assembled in the street that night. The phones of everyone in the area ring at once, and everyone turns to stare at Namie and her men while she watches in frightened apprehension.

On the roof, Celty asks the girl her name. She replies with "Celty," and Celty furiously rides her bike down the side of the building. She speaks directly into the minds of the people below, saying that she is a headless monster, real and here. Namie's men attempt to attack her but are stopped by Celty's scythe.

Seiji finds Mikado in the street and pulls out a knife. As he lunges toward Mikado, demanding the boy return "Celty," the Headless Rider steps between them and is hit instead. The two begin to fight, but the girl with the scarred neck screams for them to stop.

Upon realizing that his lover is actually Mika Harima, the stalker he thought he had killed, Seiji stares in disbelief while Mika apologizes. She tells Seiji that his sister told her how to make him fall in love with her. She received plastic surgery to make her look like the head he was in love with, and the doctor told her her name would be Celty. Seiji is furious to find Mika is not Celty's head. Izaya Orihara laughs and remarks that he could not tell the difference, so their love must not have been very strong. Mikado realizes Seiji and Mika both took a lot of risks for each other and declares that they are a perfect match.

Celty recognizes the description of the doctor who knows her name and leaves to find him. At her and Shinra's apartment, Shinra is waiting for her, and he begins answering her questions before he is asked. He tells her that he does not know whether his dad took her head, that Mika volunteered for the surgery, and that he loves her, which is also the reason he hid her head. He thought Celty's head might not love him as her body does. It is Celty's lack of a head allowing her to act so much like a human, and Shinra fears reuniting her with her head may cause her to disappear from his life.

Celty reveals her fear of dying and her worries that if someone were to destroy her head, she would be destroyed as well. Shinra finds it amusing they are both getting worked up over hypothetical situations and accepts Celty's request to punch him. In response, he knocks off her helmet so he can see the shadows that float over her bare neck.

The next day at Raira Academy, Masaomi explains to Mikado an outsider's view of the previous night's events - everyone in the Dollars met at their first ever meeting, and the Black Rider is not only real, it is in the Dollars and is headless. Seiji tells Mika that although he does not feel any love toward her, he is reminded of Celty every time he sees her, and so will continue their relationship. The pair return to school and sit together in Mikado's class.

At his apartment in Shinjuku, Izaya comments on how Namie threw away everything for her brother's love. He provokes her by reminding her that Nebula is merging with Yagiri Pharmaceuticals. To protect Celty's head, Namie resigns her position as CEO and becomes Izaya's secretary. Holding Celty's head, Izaya declares that he will start the war that will awaken her head.

Anime, Manga, and Light Novel Differences

 * Mikado does not meet Kyouhei and Saburo on his first night in Ikebukuro in the novel. Kyouhei is first introduced the next day, stopping Walker and Erika from torturing one of the kidnappers, while Saburo listens to music in the front seat of the van.
 * Mikado is stated to be 16 in the light novel and 15 in the anime.
 * The trafficking victim Celty rescues in the light novel is Kaztano. In the anime, he is replaced by Rio Kamichika. Kaztano is kidnapped later in an event exclusive to the anime, and the van gang asks Celty to help them find him.
 * Shimada is a light novel-exclusive character, while Hashim, Shiri, Hiroshi, and Ryo only appear in the anime.
 * In the light novels and manga, the group of kidnappers are lead by Gassan. In the anime, the kidnappers are Morita, Asanuma, and Kanazawa.
 * In the anime, Shuuji, Haruna, Takashi, Shiki, Sayaka and Kasuka are introduced in this arc instead of the next one. Kururi and Mairu also have a brief cameo.

Trivia

 * The manga offered to the thug by Walker and Erika:
 * Darker Than Black
 * A Certain Magical Index
 * Oreimo: My Little Sister Can't Be This Cute
 * Shikabane Hime
 * Umineko no Naku Koro ni
 * Doubt
 * Astro Fighter Sunred
 * Shakugan no Shana
 * Iscariot
 * Accel World
 * Black Butler
 * Bludgeoning Angel Dokuro-Chan