Belle, whose full name is Beilleheila Langdass, is the operator of the dungeon that serves as the primary setting of the story. She is also the boss of the tenth and lowest floor of that dungeon. Despite appearing as a young girl, Belle possesses outstanding and excessively powerful abilities that far exceed what her youthful appearance would suggest.

In terms of personality, Belle is characterized by her joyous and seemingly innocent persona. She is known for being socially inexperienced but enthusiastic, often discussing strange or peculiar topics with a matter-of-fact tone that leaves others perplexed. This eccentricity is a core part of her character, as she cheerfully and eagerly shares information about the bizarre and secretive world of dungeon management. Her behavior creates a comedic dynamic, as she acts as the straight-laced or unusual counterpart to the more stoic and reserved reactions of the protagonist, Clay. Despite her position of authority and power, Belle is also portrayed as a lonely figure who cares deeply for the continuation and health of her dungeon above all else.

Belle’s primary motivation is the efficient and innovative management of the dungeon, ensuring it remains a functional and challenging place for adventurers. Her role in the story is central, as she is the owner and manager who hires the protagonist, Clay, after Clay ventures into the dungeon searching for her missing father. She offers Clay a job, which begins their unexpected employer-employee relationship and serves as the foundation for the narrative. Belle is responsible for overseeing the dungeon’s operations, including managing monsters, stocking treasure chests, and maintaining the overall system that allows adventurers to explore.

Key relationships include her bond with Clay, which develops from a formal working arrangement into a friendship. Belle is shown to reach out to Clay as a way to have frequent contact with another human, highlighting her underlying loneliness. Their interactions, which often involve Belle explaining the intricacies of the dungeon’s workings, form the core of the story. She also works alongside other employees, such as Rangado, a dwarf responsible for finances, weapons manufacturing, and construction supervision. Throughout the series, Belle exhibits some character development as she becomes closer to Clay, with a notable moment being when the two agree to address each other on a first-name basis, signifying a growing personal connection.

Belle has several notable abilities befitting her role as the dungeon’s operator and final boss. She is exceptionally powerful, having easily defeated Clay in a duel, which convinced the experienced thief to accept her job offer. She possesses a magical mirror that she uses to monitor all activity within the dungeon, which she operates using touch and pinch controls. Furthermore, Belle can use a technique to astrally project individuals, such as Clay, into the body of a skeleton monster to battle adventurers for training or operational purposes. Her abilities also extend to management and administration, as she oversees the complex logistics of the dungeon as an operational business.