In a single night, the protagonist Himuro Kenichi learns how strong ones libido can really be.

When their parents are out of town, Kenichi gives in to temptation and sleeps with his step-sister Suzune, taking her virginity. This naturally creates a crack in their good relationship which Kenichi the morning after, in deep regret, try to repair.

However, Kenichi's abnormal sex drive makes him continue to sleep with Suzune every night. Will he manage to overcome it?