Is it bad luck to have such a seductive sister?! The brother's uncontrollable lust is planned and carried out in the defenseless space of the bathroom. At first, the sister thinks it's just a prank, but she resists in vain, becoming the prey of her brother who has become a brute. The whole story of the forbidden physical relationship that the sister cannot talk to anyone about, and the sister being devoured by her own brother, is revealed.