Kenji and his friends often go to his colleague Hiroshi's house for drinks after work, but one day, when Kenji is drunk and peeks into the bath of Hiroshi's sister, the plain-looking Umi, he is turned on by her big breasts and sexy body, and wants to do it. Kenji takes advantage of the time when Hiroshi is out and approaches Umi, who is obedient to everything he says and doesn't resist at all, so he has as much fun as he wants with the super sensitive and sexy Umi.