Agate is a character from the anime series Adventurers Who Don't Believe in Humanity Will Save the World, whose real name is Belle Huggins. Before becoming an idol, she worked as a singer in a tavern, where she was eventually scouted for her vocal talent. Her stage persona, Agate, is defined by a focus on vocal performance rather than dancing during her shows, emphasizing her strengths as a singer. In terms of appearance, she is depicted as an adolescent female with green eyes and waist-length blue hair, often styled with a side ponytail and seen wearing gloves and a dress.

The character shares a significant connection with Nick, one of the main adventurers. She initially takes a liking to him because she recognizes a kindred spirit, seeing in him a lost dog much like herself. This mutual understanding forms the basis of their relationship, which develops through multiple chance encounters in a park where they become friends. For Nick, Agate serves as a role model and an idol he greatly admires, to the point of collecting her merchandise. Their bond deepens considerably when Nick saves Agate's life, an event that transforms their friendship into a romantic relationship. As a couple, they support each other, helping one another heal from past emotional wounds, with Nick remaining her biggest supporter while loving her true identity as Bell. No information is available regarding her specific motivations, her overall role in the main story beyond her relationship with Nick, her character development arc, or any notable combat or magical abilities she may possess.