A young Keroro attempts to impress Pururu by showcasing the Kero Ball, a mysterious sphere he borrows from Giroro, who in turn borrowed it from his brother Garuru. While pressing the ball’s buttons, Keroro inadvertently transports four tadpoles inside. To escape, the tadpoles must win a pinball‑style maze. Outside the ball’s confines, a blue tadpole named Kururu discovers the Kero Ball and hears the trapped tadpoles’ pleas for help. Kururu offers to free them if he can obtain a plate of curry rice. The ball grants the promise, but the curry rice grows larger and larger until it engulfs Kururu. The expanding yellow curry slowly transforms Kururu into a “yellow devil” as the story reaches its climax.