Kiryū Keiki has four good girlfriends: figure skater Tokihara Sayuki from the calligraphy club, blonde representative of mixed blood Koga Yūka, classmate Nandzō Mao, and his own younger sister Kiryū Midzuka. One fine day the measured routine of a high‑school senior is disrupted by an unexpected find—a anonymous love letter addressed to him. Naturally, the boy awakens a serious interest in uncovering the author's identity, especially since the only clue to solving it is rather unusual—new panties left with the letter. The newly minted detective must discover new sides of his friends and uncover their fetishes. But will he be able to solve the identity of the letter"s sender? It would be nice not just to have a female friend, but a girl with whom one can date maturely.
