Makoto Usui is Rikka's friend as well as a member of the school's public morals committee. After leaving Sou-Kun's house, she comes back because she forgot her notebook but when back, she hears Sou-Kun and Rikka in their room doing sexually related things. Afterwards, she ends up in the same bookshop where Sou-Kun bought the mysterious cursing book, and Zepar seels the same book to her, which will lead to her too, having her sexual urges highly increased.