Millie is a B-rank adventurer who works as a swordsmanship tutor for Cain von Silford. She is in her early twenties and typically wears red light armor, with her red hair tied in a simple ponytail. Along with her partner Nina, she is hired by the Silford household to train the young Cain when he is five years old. Initially, she feels intimidated by teaching a child of noble status, but Cain's unprejudiced attitude allows her to interact with him more freely, and she quickly develops a playful, older-sister-like rapport with him. Although she is a skilled and experienced swordswoman, she is often humbled by Cain's extraordinary abilities, which far exceed normal human limits due to the blessings he received from the gods. Despite this, she continues to guide him in combat and adventuring fundamentals, and she often finds herself being protected or aided by him during training excursions. Over time, Millie becomes a permanent member of Cain's household, evolving from a hired tutor into a loyal guardian and trusted ally. She maintains a close working relationship with Nina, her adventuring partner and fellow tutor, and is later revealed to be the younger sister of the high-ranking adventurer Claude. Her motivations shift from professional duty to genuine devotion as she recognizes Cain's importance to the world. Her notable abilities lie in swordsmanship, and she holds the rank of B-rank adventurer, which attests to her competence and experience in combat. Throughout the story, she transitions from a skeptical mercenary to a dedicated member of Cain's inner circle, eventually moving to the capital to continue supporting his growth.