Ai is Eita's "fiancee". Ai is also Eita's childhood friend who moved ten years ago, whom he met one year before Eita met Chiwa, but returned recently. As a member of student committee, she attempted to stop Chiwa's and Masuzu's club activity due to it breaking rules, but later decided to join the club to win Eita back. During kindergarten, she confessed to Eita and the two even signed a makeshift marriage registration, making them engaged. However, nobody else except Eita and Ai know about this. She often has delusion of herself and Eita being a couple. Ai has also lied about having a boyfriend in college, and keeps a notebook like Eita's.