Kawaikereba Hentai demo Suki ni Natte Kuremasu ka?

After cleaning the Calligraphy Club room, Kiryuu Keiki discovers a love letter on the desk. Excited by the possibility of a relationship, he opens it to find the words "I like you" and a pair of panties. Believing one of the four girls who helped clean the room is responsible, he begins to investigate. The suspects include the club's president, a foreign library committee member, a tsundere classmate, and his own younger sister. Keiki is determined to find out which of them sent the letter and the underwear, hoping to identify his potential girlfriend.