Rika and Ruka are fraternal twins who love their older brother and are always fighting over him. One day, Ruka peeks at her brother while he is taking a bath and witnesses him masturbating with lotion. Taking this opportunity, she seduces her brother using her school swimsuit, lotion, and big breasts, and milks his sperm. Rika, who witnessed this scene, begins to seduce her brother in order to take him away.