Yuma, Rei and Kosei are three friends, they are known for being three inseparable and always good guys, but in reality all three of them are quite mischievous. Kosei is obviously one of them. The three of them treat their "friend" like trash, basically like a toy without feelings or life, they take her wherever they want whenever they want and do whatever they want with her. Kosei is the most mature of the group, he is also the oldest and if he says something, the others will obey.