Toppa Bashin, a vibrant sixth grader with an insatiable appetite for adventure, has one thing on his mind: Battle Spirits. He wears a ruby pendant passed down from his absent father, and every day he eagerly makes his way to school, not for academics, but for the exhilarating card game. His peers groan at his obsession, but Bashin remains undeterred. One fateful day, Bashin meets J, the child prodigy and reigning champion of Battle Spirits. J, too, wears a pendant similar to Bashin's. Bashin is in awe and challenges J to a battle. But the battle that unfolds takes an unexpected turn. The pair is suddenly transported to the Isekai World, an enigmatic arena in the clouds where the Spirits from their game come to life. Determined to pursue his dream, Bashin eagerly delves into the Isekai World, encountering other card battlers with equally unique pendants. As he climbs his way to the top, Bashin discovers that Battle Spirits is more than just a game--it's an entire world, brimming with untold secrets and mysteries.