Toppa Bashin, an energetic and thrill-seeking sixth grader, is focused on only one thing: the card game Battle Spirits. Carrying a ruby pendant inherited from his missing father, Bashin goes to school every day with excitement—not for academics, but for card battling, which greatly annoys his peers. One day, Bashin meets J, the child prodigy champion of Battle Spirits, who wears a similar pendant. Fascinated, Bashin challenges J to a battle. However, the battle he receives is not what he expected; the two are teleported to a mysterious arena in the sky—the Isekai World—where Spirits from the game become real. Sensing that his dream is finally within reach, Bashin plunges headfirst into the Isekai World, meeting other card battlers with extraordinary pendants. As he works his way to the top, he gradually realizes that there is more to Battle Spirits than he ever imagined.