3rd year, class 2. Handsome and popular, he is a tall, natural athlete and the star of the school volleyball team. He is also quite popular with many of the girls in the school. He is Akira's best friend and the the one who stabbed the pilot with a knife. He won't allow anyone to find out his secret, and was willing to as far as murdering Hikari to keep it hidden.
Arita is like the others, loving sexy women but his personality changed when he bumped his head or because of the trauma that he do into the captain of the plane. He got seriously injured causing permanent psychological effects in his mind, causing him to think that people he saw were making fun of him behind his back, so he killed them in anger. Later, Akira's group came and Mrs. Oomori got lost like Rion and her classmate. They meet each other in the cave when Arita stabs Mrs. Oomori in an attempt to murder her, but Sengoku arrives to stop him (not aware of who the killer was at the time). After finding out the killer was Arita, Akira was shocked that the killer was his bestfriend. When the wild animals began attacking, the two bestfriend carried Mrs. Oomori and they escaped the wild animals. Later the flash flood came; Sengoku and the others ran outside, leaving Arita. They saw him being carried by the water and was thought to be dead. However, in Chapter 150, Kouhei is found to be alive, with his "limiter removed".
Arita and Akira are in the same class and when he was young, he was bullied by his classmates. When Akira joinand see who is the transfer student, and why they are laughing; he saw him and he was amazed by his hair, after that they became friends. His friend Akira seemed alittle jealous of him, because he of his popularity.