Although Hida Kizuna possesses the ability to wield HHG (Heart Hybrid Gear), it is not potent enough to make him a significant asset. Nonetheless, when his older sister summons him to enroll in a strategic defense school, he obliges. Here, numerous students (most notably, buxom girls) utilize their HHG abilities to engage invaders from another realm whilst sporting barely-there pilot gear. Regrettably, Kizuna's combat skills fall short, but his sister has a unique plan - seducing Kizuna will grant the girls an energy boost. Kizuna can already sense the awkwardness looming over his new chapter of life.