Homura Ren returns to his hometown of Kaminohara after a few years away, yet he possesses no memory of having lived there other than vague flashbacks. When he retrieves his smartphone which he sent to a shop for repairs, he discovers that a mysterious game titled Monster Strike has been installed on it. Then, he suddenly gets attacked by a strange bespectacled man who summons a monster from the game into the real world. Ren’s only chance of getting out of this situation alive is by summoning the dragon Oragon, who tells Ren that he will crush the opposing monster for him. Unfortunately, Oragon turns out to be a tiny dragon that seems completely useless! However, soon Ren finds a way to use Oragon in a battle. As he fights, his memory starts returning to him.