Mitsuki Watanuki is the youngest of the three Watanuki sisters, living together in a house in the Monzen-Nakacho district of Tokyo after the loss of both parents. She is twenty years old. A prodigy in programming, she aspires to build her own IT company and views herself as the coolest among her siblings. However, her strong reliance on logic often hinders her social interactions and makes it difficult for her to connect with others. Having been the youngest at the time of her mother's death, she carries a deep, unspoken need for a maternal figure in her life, a void that subtly influences her behavior and relationships. Mitsuki is characterized by her dark violet hair and golden eyes. Within the story, she plays the role of the driven yet socially awkward sister, whose ambitions and personality contribute to the family's daily dynamics as they navigate their lives together. Her key relationship is with her two sisters, with whom she shares both household responsibilities and emotional bonds. While her precise character development is not extensively documented, her logical mindset and dream of founding a tech company define her role and motivations throughout the series. Her notable ability is her exceptional talent in computer programming, which sets her apart from her siblings.