Kôichi is a Japanese man living alone in Berlin. He has no job and hardly any friends. One night Kôichi meets Ryota at a bar which is also a sex club. Ryota came to Berlin to visit a German guy whom he had "met" on a dating app. His high hopes for romance (and marriage?) were quickly crushed since the German was only interested in sex, not even letting Ryota stay for the night. That is why Ryota ended up spending the night in the dark room of the sex club. Kôichi for some reason lets Ryota stay at his apartment. They have sex. Ryota goes out almost everyday to get laid by various local men and comes home to Kôichi's. Increasingly caught up with a strange feeling that is akin to but not quite frustration or curiosity (needless to say, it is not even close to love), Kôichi gradually gives himself up to sex with Ryota.

A highly contagious incest virus induces several generations of a Japanese family to have sex in all possible constellations and across gender boundaries – and with that man in a bear costume who suddenly appears? Only in Japan!