Kiyomaro Takamine, a brilliant yet withdrawn middle schooler, has his life turned upside down when he meets Gash Bell, a peculiar boy carrying a mysterious red book. Kiyomaro quickly discovers that Gash is a demon child involved in a fierce battle that occurs every 1000 years to determine the next Demon King. As the only one able to read Gash’s book and unlock his lightning-based powers, Kiyomaro becomes Gash’s crucial partner. Together, they embark on a thrilling journey filled with intense battles, unbreakable bonds of friendship, and unexpected moments of humor, including Gash’s odd obsession with melons.