Zatch Bell! 101st Devil

In a realm where battles for supremacy among demons have long been decided by an intricate partnership with humans, two young warriors find themselves entangled in a game-changing secret. The age-old rules dictate that one hundred demon children and their human allies would vie against each other using a set of magical books, but Gash and Kiyomaro soon discover the existence of an enigmatic 101st book, holding unparalleled power. With a quest to unravel the mysteries of Gash's past now at hand, the pair must navigate through the treacherous pathways of the demon realm. As they delve deeper into the unknown, their ultimate challenge lies in escaping the perils of this otherworldly domain and returning to help their comrades battle an adversary that appears insurmountable.