"Fifteen years ago. The so-called Entrances - tears in reality that connected the human world to another dimension - suddenly appeared all over the world. Every military on the planet suffered a horrible defeat, without even knowing who they were fighting. The Entrances vanished two weeks after they appeared, and the danger seemed to have passed. But then six months ago the Second World Collision occurred, and they came back. The world's governments evacuated to oceanic Megafloats. Only a small portion of the population was able to escape. The world is still being invaded by enemies, Magitech weapons, pouring in from the still-open Entrances..." - Principal and high commander Hida Reiri of Ataraxia

The 17-year-old Hida Kizuna visits the strategic defence academy Ataraxia at his older sister's, high commander Hida Reiri's, request. There, he encounters Chidorigafuchi Aine, a girl piloting the magical armour Zeros. When the air-raid siren wails on the Megafloat, Aine suddenly pulls off her clothes before Kizuna's eyes, telling him not to look. He on the other hand is bewildered by the exhibitionism. However, a communique from Kizuna's sister explains the seriousness of the current situation: the mission - to rub Aine's chest!? As it turns out, Kizuna has the power to level up a girl through indecent acts via his own Heart Hybrid Gear called Eros. And so, much to Kizuna's surprise, he joins Ataraxia's Heart Hybrid Gear ace team, Amaterasu, as captain, to fight in the battle against the "other world", using his unique power. In the eyes of his fellow students it does mark him as a pervert though...