Hida Kizuna possesses the HHG (Heart Hybrid Gear) ability, but it is not strong enough to make him particularly important. His older sister calls him to transfer to a strategic defense school, where many of the students (many of which are large-breasted girls) use their HHG abilities to fight invaders from another world while wearing extremely skimpy pilot outfits. Kizuna's fighting ability doesn't measure up, but his sister has another plan; getting the girls to have erotic experiences with Kizuna, so that it will allow them to replenish their energy or power-up. It looks like his new school life is going to be full of embarrassment!
(Source: MangaHelpers)
— Description from AniList community (anilist.co).
