In the near future, Japan develops an armored suit known as Infinite Stratos, or IS for short, originally intended for outer space but later repurposed as a military weapon before eventually becoming a competitive sport. The IS has one major limitation: it can only be piloted by women, or at least that is what everyone believed, until Orimura Ichika appeared. As the younger brother of the renowned pilot Orimura Chifuyu, who represented Japan and remained undefeated throughout her professional career, Ichika is the sole male in the world capable of piloting an IS. He gains admission to the IS Academy, where he is the only male student among an entirely female student body, and must train to become a pilot. He is startled to discover that his instructor is none other than his sister Chifuyu, and he is nearly irritated by the constant attention he receives as the only guy on campus. Almost every girl around him competes with the others to win Ichika's heart, and with all the flirting occurring, he barely has time to master operating his IS.