Childhood friends Nagisa and Azuma have been inseparable ever since they first spoke, always fighting. Now a high school student, Azuma has started his first relationship with a girl in his class, and is overjoyed. Behind the scenes, Nagisa has been secretly receiving advice from her about Azuma's premature ejaculation. Despite having mixed feelings, Nagisa offers to be Azuma's blowjob practice partner, calling it "training"... Is it teasing, jealousy, or...?