Nobuya, a college student in Tokyo, returns home to his family residence after a long absence. While talking with his mother, he learns that his cousin Shotaro will be visiting with his new wife, Sarina. Surprised that his quiet, unassuming cousin has gotten married, Nobuya is left utterly stunned when he first sees Sarina. Her massive breasts are almost dreamlike, with a striking cleavage that immediately captures his attention. One day, hearing soft sounds coming from Sarina's room, Nobuya peeks inside and discovers her lying exhausted after masturbating. Drawn to her vulnerable beauty, Nobuya begins to develop feelings for her—and soon crosses the line, pursuing a forbidden relationship with his cousin's wife.