An unknown type of alien called "Censor Bug" invades Earth. They plunder "H-energy" in an attempt to make mankind extinct. To save the Earth from the alien threat, high school boy Retto Enjō joins the "HxEros" team, partnering with four beautiful high school girls, one of whom is his childhood friend Kirara Hoshino. However, it turns out that Kirara has drastically changed her personality, which leads to an estrangement between the two childhood friends.