A series in which men are seduced by the temptations of their younger sisters and others. When he returns to his parents' house after a long time and tries to take a morning bath, he encounters his younger sister. She begs him to join her in the bath, but he tries to decline because it's already time for his relatives to wake up. However, his younger sister, who is curious about men's bodies, boldly invites him in, leaving him flustered... Even though he knows he shouldn't make a move, his crotch is erect. Can he keep his sanity like this?