Rei travels across the galaxy as a Card Quester, hunting for the strongest Battle Spirits cards scattered among the stars. The self-proclaimed Number One Star rides with a tiny dragon called Mugen and Salt, a robot who cooks, and he turns into Zero whenever a fight begins. When he meets the April siblings, Raira and Rikuto, who may know where the Ultimate Battle Spirits card lies, they set out together. Along the way Rei settles disputes, befriends outlaws, and clashes with the Guild, a villainous group that controls space and wants the same prize. Blending space adventure with card battles, the story slowly reveals secrets tied to the fate of the universe.