Shota-kun is a boy whose father works as a tennis coach. One day, an attractive schoolgirl older sister comes to visit his father, but when she finds him absent, Shota-kun agrees to take over the coaching in his place. The girl treats Shota-kun with surprising kindness, not only peeking at him while he changes but also touching his chest, teasing him playfully with rackets and balls, and even joining him in the bath. As her affectionate behavior continues, Shota-kun finds himself increasingly drawn to her. Eventually, during a massage session, emotions run high and their relationship rapidly escalates.