Hundred

When an extraterrestrial organism known as "Savage" attacks mankind, the only technology capable of combating the enemy is a weapon known as “Hundred.” A survivor of a Savage attack, Hayato Kisaragi is a teenager boasting the highest compatibility level with the aforementioned technology and as a result, is invited to master his skills at Little Garden, a prestigious military academy aboard a battleship. Over the course of his intense training for the battle ahead, he immediately attracts the interest of multiple female peers and gets drawn into a number of incidents as he tries to fight against the creatures that now inhabit Earth and threaten its safety. A mysterious life form known as Savage is attacking the Earth, and there is only one weapon that can counter it: the Hundred. To become a Slayer, a master of military arts who wields this Hundred, Kisaragi Hayato enrolls in the marine academy city ship Little Garden. However, Hayato feels a strange yet familiar sense of incongruity towards Emile Crossford, his roommate who somehow knows him from somewhere. On top of that, as soon as he enters the school, he is challenged to a duel by the Queen, the school's most powerful Slayer, Claire Harvey.