The protagonist, Akiho, is on his way home with his quiet busty girlfriend Suzune when suddenly, an outgoing blonde gal appears in front of them! She gets all familiar and flirtatious with them as if she knows them very well. Turns out, the gal is actually Sayu, who used to be an introvert just like them! When Sayu finds out that Akiho and Suzune are still inexperienced in the bedroom, she calls together her gal friends to give them sex training for their first time...