Rio is of average build for a teenager. She has brown eyes and hair usually worn in pigtails. She is shown wearing two pink flower hair clips, a white blazer, dark red shirt (possibly magenta, a faint reference to her username) 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.
Rio discovered that her father was cheating on her mother, and she began thinking about what would happen if she disappeared. In an online chat room, she meets someone who goes by the name "Nakura" who wants 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 wants to disappear with him.
Mika Harima Arc
Rio leaves home feeling confident about her decision and wanting 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 feels unsure initially, but she follows him into an alley and is kidnapped by the man and two of his friends. She is thrown into the back of their van and knocked out with gas. 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 nearby a building. When Celty drops her off, Rio heads up to the roof and finds the real Nakura, Izaya Orihara.
Izaya toys with Rio, admitting to her the whole truth of his actions and motives, before bringing Rio to the edge of the building, where the bloodstains from the last person who committed suicide there are still visible on the ground below. He forces her to reconsider whether or not she really wants to disappear. Rio tries to slap him, and he catches her before she falls. After he walks away, bored, Rio jumps, only to be caught in Celty's shadows. Afterward, Rio changes her point of view and decides to forgive her parents.
When she is interviewed on the street by Shinra, who asks her about the Black Rider, she denies knowing anything about the urban legend.
Dollars and Blue Squares Arc
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 Arc
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).
- The name Rio means "white jasmine" (莉, ri) and "thread" (緒, o). The surname Kamichika means "god" (神, kami) and "near, close" (近, chika).