Reiji has always been pushed around by his expressionless childhood friend, Tsubomi Mochizuki, whose thoughts are often a mystery. Suddenly, she asks him to be her practice partner for sex because she has a gotten a boyfriend. Reiji, who is in love with Tsubomi, has no reason to refuse and begins the practice. However, Tsubomi believes in her own rule that "kisses should only be shared with someone you love," so she won't let him kiss her. While she was expressionless at the time, she gradually learns pleasure and begins to show erotic voices and expressions, making it impossible for Reiji to hide his emotions...!
