Mirelle is a thief and one of the three original adventurers in the party that eventually includes the mage Louie. She works within the Thieves' Guild of Orphan in the city of Phan, where she belongs to a group of pickpockets known as the Cats. As the youngest member of the main party, she is small and agile, fighting with two small daggers that she wields with quickness and precision. Her temperament is best described as frenzied: she is easily provoked, quick to anger, and particularly short-tempered with Louie, whose unconventional and often reckless behavior constantly frustrates her. Despite this fiery nature, she is highly resourceful and able to think on her feet during dangerous situations.

Mirelle's motivations center on her livelihood as a thief and adventurer; she values competence and practical results, and she initially resents the divine revelation that led the priestess Melissa to recruit Louie into the group. Over the course of the story, she becomes a reliable if grudging member of the team, learning to work alongside Louie despite her ongoing exasperation. Her relationships within the party are marked by contrast: she shares a bond of professionalism with the fighter Genie and the priestess Melissa, but her dynamic with Louie is defined by frequent arguments and comedic clashes. Nonetheless, she remains loyal to her companions and contributes her thieving skills to their quests. In terms of development, Mirelle gradually becomes more accustomed to the group's odd rhythm, though her quick temper and pragmatic outlook remain consistent. Her notable abilities include expert lockpicking, stealth, trap disarming, and rapid close-quarters combat with her daggers, marking her as a nimble and cunning rogue.