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.

描述一个被神秘生命体“Savage”侵略的世界，唯一能与之抗衡的只有名为“百武装”的兵器。少年如月隼人为了成为操纵百武装的武艺者，决定进入海上学园都市舰“Little Garden”就读。入学后的隼人遇见一名陌生却对他所知甚详的室友艾米尔·克劳福德，还对她有着一股淡淡的怀念感。此时，隼人收到来自学园最强、拥有女王称号的克蕾亚·哈维的决斗要求……

《ハンドレッド》――それは地球を襲う謎の生命体《サベージ》に対抗できる唯一の武器。《武芸者（スレイヤー）》を目指すため、海上学園都市艦《リトルガーデン》に入学を果たす。だが――なぜか自分のことをよく知るルームメイト、エミール・クロスフォードに、どこか懐かしい違和感を覚えるハヤト。さらに入学早々、学園最強の武芸者《女王》クレア・ハーヴェイから決闘を申し込まれてしまい……!?