High school student council president Hotaru Tachibana—a girl often confused as a boy due to her speech pattern and clothing—is not afraid to fight against injustice. When her friend is supposedly swindled by a host, Hotaru feels compelled to confront the man responsible. He turns out to be her next-door-neighbor, Masamune Matsuoka, who decides that the best way to settle this is to play a "survival game": an imaginary war game where fake guns are used, but the battles are no less real.

Despite Hotaru's best efforts, she ends up losing and incurring a large debt due to the resulting damages. Consequently, she is forced to become the third member of Masamune's male-only team "Toy ☆ Gun Gun," joining his friend, Tooru Yukimura, an author of adult manga who dislikes her at first. However, before she even notices it, Hotaru becomes genuinely fond of both the sport and her team members. She chooses to share in their dream of becoming the best survival game team in Japan and winning the famous tournament, Top Combat Game, even if that means hiding her identity as a girl from her teammates.