Manami Mamiya

Manami Mamiya (間宮愛美, Mamiya Manami) is a supporting character in Durarara!!

She appears early on as one of two girls whom Izaya met to commit suicide together and is humiliated when Izaya learns of her petty reasons for wanting to end her life. She appears again, over a year later, as a member of Izaya's alliance in order to get an opportunity to get revenge on him for deceiving her.

Characteristics
Manami's appearance in the manga consists of a plain T-shirt and skirt with a light coat. She has shoulder length black hair, some of which is held back by a hair clip. Her appearance in the anime is vastly different, presumably to make her stand out more. Her hair is a short reddish-brown with one side tied into a small pig tail. Her outfit consists of a black sweater with a pink jacket that appears to have the sleeves ripped off. She also wears glasses and sports a necklace that looks like an eye.

In her first appearance, Mamiya appeared depressed, mentioning a recent breakup as her reason for committing suicide. After Izaya's deception and during her later appearances, Mamiya is shown to be vindictive, vowing to kill Izaya over humiliating her. The novels describe her hatred for Izaya and desire for revenge being the only things that keep her wanting to live.

In terms of abilities, Mamiya possesses no abnormal strength or skills. However, she is shown to be very clever at times, being able to convince Haruna Niekawa to hand over Celty's head in order to expose it to the public.

Background
Not much is known about Mamiya's past before the start of the series other than that her boyfriend dumped her for another woman. This caused her to sink into a deep depression which drove her to want to attempt suicide.

Dollars/ Mika Harima Arc
Manami appears along with Izaya and an unnamed woman in a karaoke booth sharing one last drink before they end their lives. They each discuss their motives for committing suicide as well as the best method to use. Izaya then asks what the two of them will do once they die, with Mamiya expressing her belief in the afterlife. Izaya appears exasperated with their responses, calling them hypocritical for wanting to end their current lives and expecting a better one in return. The unnamed woman quickly picks up that Izaya has no intention of dying, which he admits to. The two girls are naturally offended, but Izaya once again calls them hypocrites, saying they should not care what anyone does to them since they are going to commit suicide anyway.

Izaya soon gets a call from an unknown individual, informing him that they would arrive soon. Izaya hangs up and points out several key details about the room they were in, primarily the person sized suitcases underneath the table as well as the fact that he had drugged their drinks earlier. The two girls assume that Izaya is planning to sell them to human traffickers and cry out for help, but the drugs in their drinks kick in. As Mamiya passes out, she swears vengeance on Izaya. The information broker expresses some joy at this as he tells her that hate alone can motivate her to live. Eventually, Izaya tells Celty to drop them off on a park bench somewhere.

Daily Life
When Izaya's hospitalization is announced on the news, Mamiya uses this as her opportunity to get revenge. When she visits him at the hospital, Izaya is initially unaware of who she is, saying she was one of many girls he played the suicide prank on. Upon hearing this, Mamiya simply attacks him with Izaya easily disarming her despite his injuries. As Izaya slowly remembers who she is, he starts laughing uncontrollably, impressed that Mamiya managed to hold on to her hatred for so long. Reinvigorated with his love for humanity, Izaya offers Mamiya a job for her to bear witness to what he was about to do. Mamiya accepts, seeing it as a way for her to get another opportunity at revenge.

Adabashi Arc
Mamiya is made Namie's assistant after Izaya cements his alliance. Izaya explains that even Namie needs help processing all the paperwork that has built up over the past few months.

Volume 11
Mamiya decides to steal Celty's head to try and throw a wrench into Izaya's plans. As it was Haruna's turn to guard the head, Mamiya goes to her apartment to attempt to persuade her to hand it over. Haruna agrees to hand over Celty's head as it would allow her to continue her search for Takashi Nasujima.

Trivia

 * While the first season of the anime depicted Rio Kamichika as Izaya's online suicide victim contact and the manga depicted Manami and another, unnamed girl as Izaya's online suicide victim contacts, it is implied in the novels that both events occurred, as both girls are present. Later on, in Durarara!! x2, Manami is introduced into the anime as well, along with her past regarding Izaya, because of the critical role she plays in the future plot. It is implied that Rio's incident occurred before Manami and the other girl's, because after meeting Manami at the karaoke bar, Izaya proclaims he is bored with his hobby of finding online suicide victims.