Ryuuhei Oda saw his caring elder brother's death as a child, as well as a mystery mark left beside his body. The lively and impetuous young guy, now a second-year high school student, spends his days doing what he enjoys most—kickboxing. A mysterious thing bites Ryuuhei's leg on his walk home one night, causing him to have a disturbing dream filled with unusual beings. When he is attacked by the same creatures the next day in the real world, Jessica Clayborn and Aruto Fushibe rush to his aid, saying Ryuuhei is their new member. Faced with an impending threat, Jessica pushes a befuddled Ryuuhei to turn into a "knocker-up," a person capable of confronting the monsters.