Blue Flag Vol. 5 (manga)

School is back in session after summer break, and Taichi and Futuba are slowly transitioning their relationship from friends to something more. Suddenly, Mami starts being unusually friendly with Taichi, leaving Futuba feeling anxious. Taichi, unsure of Mami's true intent, can't help but get dragged along in her wake. Their situation attracts attention, more people become involved and soon everyone is questioning everyone else's relationships!