Eru, a sexy, hot-bodied woman living in the same apartment building, has been arousing Kenji and others with her seductive clothes and provocative attitude. One day, caught in a sudden downpour and completely soaked, she realizes she's locked out of her apartment and comes to Kenji's place. Wanting to warm her chilled body, she suggests taking a bath. Unable to resist, Kenji peeks—and the story begins from there.