Energetic and thrill-seeking sixth grader Toppa Bashin has his mind set on only one thing—the card game Battle Spirits. Bearing a ruby pendant inherited from his missing father, Bashin heads to school every day with excitement: not for academics, but for card battling, much to the chagrin of his peers.

One day, Bashin encounters J, the child prodigy champion of Battle Spirits, who bears a similar pendant. Star-struck, Bashin challenges J to a battle. However, the battle he gets is one he did not anticipate; the two are teleported to a mysterious arena in the sky—the Isekai World—where Spirits from the game become real.

Feeling that his dream is finally within arm's reach, Bashin dives headfirst into the Isekai World, encountering other card battlers with extraordinary pendants. While making his way to the top, he slowly realizes that there is more to Battle Spirits than he ever imagined.