Kawarada Hitomi

Hirose Kazumi, the school’s beauty, is in love with her older sister’s boyfriend. When she learned that they are getting married, she hooks up with Yamamura from her class whom she’s been having eye contact lately. They become sex buddies with a condition that their relationship must be a secret from school and that they won’t fall in love with each other.

Riku likes her sensei but a mysterious young boy of her age who looks strikingly similar to him steals a kiss from her, how will the story of the "Ubawareta Kiss" unfold?