Arata takes the appearance of teenage girl with brown eyes and also brown hair ending in short pigtails. She wears a red school gym uniform with her name across the chest, and white shoes with blue stripes.
She is extremely rash to the point where she forced Mato to sprint even though she was only showing interest in the basketball club. She is also fond of draconian training, and supposedly nobody is able to play against her one-on-one.
She is very hyper and bold, and very tomboyish. However, she has many insecurities, but she tries to cover them up by acting strong. She believes that she shouldn't blame anything bad on anyone else, since that would mean that they would be the ones having responsibility for fixing it and she wishes to take on that responsibility.
She has a crush on a boy in her school. She initially has insecurities about confessing to him, at one point blaming it on not having "big boobs" like Saya Irino, but eventually confesses to him. However, she tries to pretend like she didn't in front of the others.
Her peers tend to call her "Koha'chi". She in turn refers to Yuu Koutari as "Underfoot".
Mato eventually joins and Arata, impressed by her basketball talents, decides she should be a semi-regular for the basketball tournament. Later, Mato and Yuu catch her giving a love letter to Takuu.
She hauls Mato into intensive training, despite protests from others, saying that she will do fine even if she doesn't fit the team's niche. However, once they return to school, she finds her love letter publicly displayed on the school bulletin and some boys, carrying Takuu in a strongarm, teasing her about it. Her friends try to defend her, but she proclaims that it is a mistake, and laughs and walks away, hiding her pain.
She goes to Saya's room and says that she shouldn't do things she's not good at, but suddenly sees Saya looking at her with a dark expression and crying. Instead of comforting her, Saya tells her that she must be strong to hide her pain like that, because the entire school is laughing about her, that she's the laughingstock of the entire school.
Some time later, she accidentally trips during basketball practice, and twists her ankle, detrimental as the tournament is soon. Even though she claims she will be fine, Mato takes her to the infirmary, and says that she'll get a teacher to help; however, Arata protests at the mention of Saya.
While Mato is walking away, Black★Rock Shooter beheads a mysterious person that Black★Gold Saw had created from her watering pot, and Arata clutches her head and screams. At that moment, both Mato and Saya sense something. Mato runs back to the infirmary, only to find Arata lying prone on the floor.
Later, Arata is shown to have recovered with nothing more than a sprained ankle. However, similar to Kagari Izuriha, the decapitation of her other self has caused her to forget her feelings for another person, in this case Takuu. No longer feeling anything for Takuu, she rejects his feelings for her.
After Insane Black★Rock Shooter's defeat results in her "other self" being brought back, she is implied to have started dating Takuu, as she is seen walking to school with him and hanging out with him.
- The official website, prior to the anime's start, listed Arata's name as "Arata Obata".
- In the third episode of the anime, the girl that Black★Rock Shooter had killed could possibly be connected to Arata. She resembles Arata, and Arata fainted after the girl was beheaded similarly to Chariot. She may possibly be Arata's "other self". This is supported by the fact that the girl's death erased Arata's feelings for Takuu, similar to how Kagari's feelings for Yomi disappeared or decreased after Chariot's death.