Kon'yakusha Higuchi Tsukiyo no Himitsu -Kakusareta Shin'yuu to no Aida no Seiseikatsu-

Synopsis

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 Ichiha began dating the only woman in the group, Higuchi Tsukiyo, and as adults, they got engaged. It was Tsukiyo who confessed to him. Thanks to the support of another man in the group, Konoe​ Seiki, the three of them continued to get along like always. During the day, they hang out as usual; at night, Ichiha and Tsukiyo have sex.

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

"It's not cheating. That was before we started dating."

As the intimate relationship between Tsukiyo and Seiki comes to light, their twenty-year-long friendship starts falling apart.

The relationship of men and a woman who have spent more than half of their lives together; due to pleasure and discrepancy, it creates an essence of dilemma...