Rio is of average build for a teenager. She has brown eyes and hair usually worn in pigtails. She is shown wearing two flower hair clips and wears a pink shirt, white cardigan, and jean shorts when going out. She is also shown wearing glasses at home.
Rio is a rather melancholic girl with a cynical view on life. Initially, she felt that no one was paying any attention to her and wished to die. After Celty's intervention, she gets a new lease on life and approaches the world with a more positive outlook.
Dollars/Mika Harima ArcEdit
After she discovered that her father was cheating on her mother, Rio began thinking about what happened if she disappeared. While online in a chat room, she runs across someone who goes by the name "Nakura" (who is Izaya Orihara) who wanted to disappear as well. Feeling a connection with him, Rio begins chatting regularly with Nakura. She tells him about her problems, and he bares his soul to her, as well. One day, while Rio is sitting in her room, she receives a message from Nakura, asking if she wanted to disappear with him.
When she leaves her house, Rio feels confident about her decision. She wants to see the face of the person who feels the way she does. Out on the streets of Ikebukuro, a man approaches Rio, claiming to be Nakura. She follows him into an alley, and ends up being kidnapped by the man and two of his friends. She is thrown into the back of their van and knocked out, not knowing that Izaya was the solitary witness. Celty Sturluson ends up coming to Rio's rescue in order to give her a message that someone is waiting for her on the roof of a building. When Celty drops her off, Rio heads up to the roof and finds the real Nakura, Izaya Orihara.
Izaya goes on to mess with Rio, telling her that he is the one who had her kidnapped, but also the one who had Celty save her. Rio asks him why he did it, but Izaya just gives her a cryptic answer: because he likes humans. Izaya then brings Rio to the edge of the building, asking her if she still wants to disappear. He tells her to look down at the ground, where she sees the blood stain of the last person who committed suicide. He tells her that, if she jumps, her odds of survival are slim. He also says that the suicides stem from different problems, but that all those people leave the world in the same way.
Izaya's words upset Rio and she tries to slap him. However, she misses and almost falls over the edge. Izaya grabs her by the wrist and lets her look down for a bit, as he is the only thing keeping her from falling. He asks if he should let her go, and she doesn't answer. He proceeds to bring her back to the safety of the roof, and walks away, saying that this whole ordeal was boring because it went exactly according to his plan. He then tells her that she's just as ugly as the rest of the world, and leaves her on the roof. Rio thinks about jumping, but she hesitates. In the end, she jumps anyway, only to have Celty help her again by using the shadow of the stairs to break her fall. Rio then asks why she saved her. Celty responds with a message that says "Because the world isn't as terrible as you think."
Afterwards, Rio decides to forgive her parents. She changes her point of view on life and decides she wants to share those words with someone someday.
She is interviewed by Shinra, who asks her about the Black Rider.
Dollars and Blue Squares ArcEdit
Rio is seen hanging out with her friends, one of whom is Non, the girlfriend of Chikage Rokujou, and she spots Anri and Akane in the crowd, waiting for someone. She walks over and invites the two of them to hang out but Anri declines, explaining the meet up she had planned with Mikado and Aoba. Rio says goodbye and she and her friends go to a nearby cafe. A few hours later, Izaya as "Nakura" posts a message on the dollars forum saying that they should kidnap Chikage's girlfriend Non to make him stop the attack on the Dollars.
Rio and the other recognize themselves as the targets and decide to leave the cafe. They are cornered in an alleyway and are forced into a van. Rio sees Mikado try to rescue them but he ultimately fails. Rio and her friends are then taken to Raira's practice fields where Rokujou and Kyouhei are fighting.
As the girls watch the scene unfold, their kidnappers are distracted by a bright flash of light which gave ample time for Walker and Erika to swoop in and save them. The girls flock behind Walker who holds the rogue dollars at bay with a lighter and a can of spray paint. After the fighting ends, Rio and the others are presumably escorted back home.
Daily Life ArcEdit
She and her parents decide to go shopping. She passes by Manami, who was caught in a similar circumstance as her thanks to Izaya.
- While the first season of the anime depicts Rio as Izaya's online suicide victim, in the light novels it is actually Manami Mamiya and another unnamed girl who fall for Izaya's trick. 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.
- Rio's email handle is magenta-amethyst. In the anime, it is pronounced "Mazenda."
- Rio is the only minor character to appear as a playable character in Durarara!! Relay.
- Rio has been kidnapped due to Izaya's schemes twice in the series so far. In Durarara!! Relay, the players can prevent Rio's kidnapping if his relay points are lower than the others (e.g. if the relay points for Aoba are higher than Izaya, he will stop him from kidnapping her).