Kida Masaomi is a childhood and best friend of Ryugamine Mikado. He is the outgoing and active counterpart to Mikado's sheltered lifestyle. Very at home in the city of Tokyo, he serves as a guide to Mikado.
Masaomi Kida is a childhood friend of Mikado Ryugamine as the two grew up together as kids. Some time before the series started, he moved to Ikebukuro to go to middle school there. However, while he was there, he got caught up in the color gang wars and created a color gang called the Yellow Scarves. Things went well for a time until he was introduced to Saki Mikajima and Izaya Orihara. Even though he is wary of Izaya even from the first time they met, Izaya's supply of information greatly helped Masaomi in his battles with the Blue Squares. Unfortunately, Saki was attacked and injured by the Blue Squares, thus leading Masaomi to quit the Yellow Scarves and vowed to never go into the "dark side" again.
Some time later, Masaomi invited his friend Mikado to go to Ikebukuro and enroll to Raira Academy. This starts to cheer his life up, as he once stated that Mikado is the reason he is himself again. Due to his involvement in gangs, Masaomi knows every strong figure in Ikebukuro who are not to be crossed for any reason and warns Mikado.
Masaomi Kida was created by Ryohgo Narita for the purposes of the light novel series Durarara!!. Kida made his first appearance in Chapter 1, Volume 1 of both the light novel and the manga. His anime counterpart was created by Takahiro Omori. He is voiced by Mamoru Miyano in the Japanese version and Bryce Papenbrook in the English version.
In the start of the series, Masaomi acts extremely chipper and light hearted about many things in his life. He constantly attempts to woo the different girls at his school but always fails miserably. It is shown that he cares a great deal for his friend Mikado and Anri Sonohara, who he met through Mikado. Even when the three are together, he always acts carefree and that there is nothing wrong with anything in the world. He sees the relationship he has with Anri and Mikado as a three way love triangle in which he cares for Anri deeply and will do anything for her.
In reality, he feels alone a lot of the time and feels depressed about the way life has turned out for him. He tries to protect his friends from the darkness of Ikebukuro but feels helpless when they get drawn into things as well. Masaomi also feels guilt over the attack on his girlfriend Saki that took place around a year ago as a result of the gang violence and what little he did to prevent the attack. He harbors a deep hatred for Izaya too since he knows he is behind anything that goes on in Ikebukuro and is partially responsible for Saki's attack.
Masaomi is the first person to welcome Mikado to his move to Ikebukuro. On the first night there, he shows him around the town and highlights different venues and shops. He also introduces Mikado to Kadota, Walker, Erika, and Saburo; four friends of his he has known for a while now. They also pass by Simon Brezhnev, the local owner of the sushi bar. Masaomi warns Mikado that the streets can be dangerous at times. Even though the color gangs have disappeared, there are always rumors about the Dollars in the city and what they'll do. Masaomi informs Mikado that there are two people he should never cross: Izaya Orihara and Shizuo Heiwajima. Mikado wonders who Shizuo is as they see a vending machine flying in the distance, Masaomi indicating that was the work of Shizuo. The two get a glimpse of the Headless Rider as she drives down the road, Masaomi explaining the urban legend behind the rider.
School starts for the two as they go to Raira High School for their academic career. They find themselves in separate classes but often walk to school and go home together. When Mikado becomes class representative with Anri, she becomes a part of the group that they hang out with. This escalates after Mikado asks about the Dollars and the two friends encounter Anri getting bullied by a group of ganguros that go to their school and a so-called member of the Dollars. Izaya appears and lends a hand on the trio by harassing Anri's offenders. After a brief introduction of themselves, Shizuo got into the mix, assaulting Izaya first and then beating up the gang members that tried to attack them. This leads Mikado to escape with Anri, leaving Masaomi behind.
Masaomi then hangs out with Mikado and Anri in the next following days. After their ice cream eating with Anri, that night Mikado bumps with a mysterious girl who was seemingly chased by the Black Rider. In their school days, they investigates about the members of the Dollars, and makes Ryo Takiguchi admit that he is a member of the Dollars.
Masaomi stills acts like a clown especially when he helps Anri avoid a perverted teacher of theirs. It is at this time he admits he feels alone and he must protect Mikado from the darkness of the city. While he walks around town, he almost gets jumped by a group from the Yellow Scarves but is helped out of the situation by Mikado who are able to escape thanks to Celty. As time goes on and the dilemma over Celty's head escalates, Masaomi is not involved as he is too busy trying to figure out who in the school is a member of the Dollars. Masaomi also admits to avoiding Saki as long as he can.
After the flash mob meeting of the Dollars, six months pass as Ikebukuro is becoming the home to the Yellow Scarves once more. A group of Scarves approach Masaomi with an offer about something but he declines. It is at this time that the Slasher attacks start to occur around the city where people are attacked but not killed. Masaomi is concerned about Anri since one of the Slasher attacks almost got to her since the assailant attacks the ganguro bullies from earlier.
Things heat up when Haruna Niekawa attacks Anri who admits to being the Slasher. Even though Anri defeats her, she is still badly wounded and taken to the hospital. Masaomi and Mikado visit her as Masaomi vows revenge for Anri. He goes to the docks where the Yellow Scarves are based out of and announces his plans to lead the Yellow Scarves once more, indicating that he was the original leader before they disbanded. He says that he is doing this to get the Slashers for what they did to Anri and will take down the Dollars too if they have a part in this. What Masaomi doesn't know is that Anri is actually the mother of the Slashers.
In the ensuing months, Masaomi works with the Yellow Scarves to figure out who leads the Dollars and the Slashers and how to get back at the latter. He hates working with Horada who is extremely violent and wants to beat up random people even though no one knows who anyone in the Dollars is. It is revealed through a flashback that he came to know and date Saki through Izaya and Saki was kidnapped by their rival gang the Blue Squares. Izumii, their leader, broke both her legs and told Masaomi to come and face off to save her but he froze up. Kadota and his group leave the Squares and save Saki, never telling her what happened with Masaomi. Saki was able to testify though against Izumii as he went to jail for aggravated assault and broke up the Blue Squares. Masaomi disbanded the Yellow Scarves as a result of this before going to high school.
Masaomi then tries to gather more information about the Dollars and keeps his gang from attacking, even though Horada repetitively suggests to him that they should. One of his gang members tells him the rumors about how the Black Rider may be the Slasher since she is also known as a member of the Dollars. Masaomi tries to investigate but when Anri sneaks in to their base to find out whats wrong with Masaomi, she freaks out and leaves. Almost getting caught, she is saved by Celty and uses her blade to evade attack. Masaomi is now 100% certain that the Slashers are members of the Dollars. He was forced to seek Izaya's aid, and was revealed to him that his best friend Mikado is the leader of the Dollars.
Unable to process all the information, Masaomi tells everyone to stay put while he figures out what to do. Horada becomes impatient and begins to start attacks on random people in hopes of hitting the Dollars. Anri is able to stop some of the attacks since she has control over the Slasher victims and is able to rescue some people. However, she was spotted a few times as they tell Masaomi about the Slasher being a girl with glasses, a Raira uniform, and big boobs. Masaomi pieces together that Anri is the Slasher and confronts her after the Dollars help her escape from the Scarves. He gets ahead of himself and offends Anri by telling her that she's a seducer and gets slapped before she runs away.
Masaomi continues to figure out what all this means and makes brash assumptions about Mikado and Anri that he is disgusted by. Horada calls him to tell him he has been ejected from the Scarves and now he is an enemy. They also know Mikado is the leader of the Dollars and begin to plot to attack and kill both of them. Horada goes as far as to gun down Shizuo and blame it on Masaomi. Masaomi takes responsibility to protect his friends and rushes to the Yellow Scarves' hide-out, but was stopped by Simon. Simon tells him that he knows what he's going to do and must not do it, but Masaomi insisted, saying it's the only way.
At the base, Masaomi confronts Horada and puts together that he was Izumii's partner and that most of the new members of the Scarves were also Squares. The gang seems to be intimidated as Masaomi fights his way through them and almost gets to Horada, but is knocked out first. Before Horada can kill him, Anri breaks into the base with Celty and Mikado right behind her. They look to be cornered but Kadota emerges and begins a counter attacked as the Dollars had blended in the Scarves since no one knows who is in the Dollars. Mikado and Anri are able to get Masaomi to the hospital with the help of Saburo, Erika, and Walker as Celty, Shizuo, and Kinnosuke take down Horada.
When he wakes up in the hospital, Saki meets him to reveal that she was caught intentionally by the Blue Squares and feigned being crippled because Izaya told her too. Saki tells him that she already severed her connection with Izaya and will no longer obey him. Masaomi knew the whole time as he vows to leave Ikebukuro with her once they are better. Mikado was then seen traveling with Saki happily, and things temporarily goes back to normal in Ikebukuro. Even with Masaomi gone, Mikado knows he will come back as he is able to communicate with him with Masaomi using the alias Bakyura.
While he was away, Masaomi and Saki worked for Izaya despite of the chaos that happened in Ikebukuro. They was sent on a remote village to investigate about a man named Yodogiri Jinnai, which made Masaomi suspicious. Saki told him to go to Mikado and Anri himself so that he would be at peace, but he says can't just see them because they might not accept him anymore.
After they return in their place, Kida discovers that Izaya hacked his Dollars account and talked to Mikado. He then calls him and after being insulted and saying his rage, Izaya hangs on him curtly. After a few hours, Saki tells him that he's lonely. She then said that she can be his lover, but she can't replace Anri and Mikado. They would never abandon him, and if they did, she would be there for him. If they are in trouble, she should help them himself. Masaomi was moved and understands and went to Ikebukuro to find Mikado.
Masaomi was seen again witnessing Mikado in tears apologizing to Chikage. He decides that Mikado doesn't want him to see himself like that and leaves. He would just reintroduce himself when Mikado is alright again.
Masaomi learns that Mikado and Aoba Kuronuma are hunting rouge Dollars and tries to prevent Mikado from doing something stupid. He tries to apologize to Shizuo, but he was sent flying out cold, waking an hour later. He later finds Mikado badly beaten by Adabashi Kisuke. Masaomi tackled Kisuke long enough for Mikado to set him on flames. Masaomi was shocked by Mikado's brutality, and is greatly disturbed and angry when Mikado smiled at it. He yells at Mikado, who brushes him off and leaves.
He then eventually meets with Anri, and they had a cheerful and fun reunion. Masaomi then decides to bring the Yellow Scarves back to annihilate that remnants of Blue Squares who infiltrated the Dollars and, most importantly, remove Mikado from his evil side.
Masaomi still went in the Dollars Chatroom, trying to contact Mikado who leaves off. He then went to Russian Sushi to find Kadota Kyohei for his advice. He tries to convince them to quit the Dollars and join the Yellow Scarves. Kyohei said that they have to think about it. Masaomi tells him that he will never try to fight them because they are stronger than him, before leaving.
Kyohei suffered a coma when he was been on a hit-and-run with a car, greatly shocking Masaomi. He later then regroups the most loyal Yellow Scarves members and planned on waging a war against the Blue Squares to save Mikado, despite his comrades' dislike about the idea. Walker suddenly appears with a Yellow Scarves member named Yatabe. He asks Masaomi if he is the one behind Kyohei's assault. Masaomi assumes that Walker suspects him, but was told that the question only meant what it meant in literal. When Walker left, Masaomi smells kerosene and warns the others. Walker came back, but didn't answer Masaomi's question.
Masaomi feared for the safety of the members of the Dollars, and decides that he will do anything bring Mikado back to normal no matter what.