Kiryuu Keiki finds a love letter tucked inside a pair of panties left in the calligraphy club room, and with best friend Akiyama Shouma's help sets out to identify his secret admirer among the girls at school. The candidates line up quickly: Tokihara Sayuki, Koga Yuika, his adoptive sister Kiryuu Mizuha, and transfer student Nanjou Mao. Each turns out to hide a fetish stranger than the last, complicating Keiki's search for a straightforward answer.