When humanity faces off against extraterrestrial creatures called 'Savage,' their only defense lies in the powerful weapon known as 'Hundred.' Hayato Kisaragi, a rare survivor of Savage attacks, possesses unmatched compatibility with this technology, earning him a spot at the esteemed military academy, Little Garden, situated on a battleship. Amidst rigorous training to combat the alien threat, Hayato finds himself entangled in the attention of several female classmates and embroiled in various conflicts against the Savage endangering Earth's existence.