When he was little, Ryuuhei Oda witnessed the death of his caring older brother, along with a mysterious mark that was left near his body. Now a second-year high school student, the outgoing and impulsive young boy spends his days doing what he loves most—kickboxing.

One night on his way home, a peculiar creature bites Ryuuhei's leg and causes him to have a strange dream filled with odd entities. When he is attacked the next day by the same creatures in the real world, Jessica Clayborn and Aruto Fushibe come to his rescue, claiming that Ryuuhei is their new recruit.

Faced with an imminent threat, Jessica urges a confused Ryuuhei to transform into a "knocker-up," a person with the ability to confront the monsters hailing from the dreamscape. Using his talent for kickboxing to his advantage, Ryuuhei awakens his powers to save the city, only to come across a familiar mark—a mark that he could never forget.