Shinomiya Kyouya is compelled to join the GJ, an enigmatic club that engages in duels within a room of a certain school's former building. There, he encounters the club president, Mao, a petite girl with a commanding presence; Mao's younger sister, Megumi, who possesses the heart of a bipolar angel; Shion, a recognized genius lacking common sense; and Kirara, who is perpetually hungry and mysterious. Time passes quickly surrounded by these distinctive girls.