婚約者・樋口月夜の秘蜜

20 years of friendship──Now all grown-ups, a group of two men and one woman were still close friends. When he became a college student, Sonoda Ichiyou began dating the only woman in the group, Higuchi Tsukiyo, and now as adults, they got engaged. It was Tsukiyo who confessed to him. Thanks to the support of another man in the group, Konoe​ Hoshiki, the three of them continued to get along like always. During the day, they hang out as usual, at night, Ichiyou and Tsukiyo make love as lovers.

One day, when everything is going well, Ichiyou happens to borrow a laptop from Tsukiyo, on it, he discovers a "homemade video of a man and a woman having sex." And the people in that video are Tsukiyo and Hoshiki. Feeling dizzy from the shock of finding out his lover's affair, Ichiyou confronts her, but he gets an absurd answer from Tsukiyo.