Mari Tokumitsu is a supporting character in the series. She is the aunt of the protagonist Shintaro Tokumitsu and the owner of the studio apartment where he lives. She is a professional manga artist who debuted at the age of eighteen and works for the publishing company Square Emix. At twenty-eight years old, she has long hair, wears glasses, and has pink hair and violet eyes.

Her personality is cheerful but carries a distinctly childlike quality. Despite her demanding career, she maintains a playful demeanor and often teases her nephew about his personal life, frequently leaving him embarrassed. Her profession, however, takes a heavy toll on her daily habits. She regularly loses sleep and skips meals in order to meet tight deadlines, leading to a somewhat chaotic lifestyle. Though her work keeps her extremely busy and she does not get much time to see Shintaro, she makes an effort to check in on him whenever she gets the chance.

Her primary motivation is her work as a manga creator, which drives most of her actions and decisions. Her role in the story is that of a landlord and family member who provides Shintaro with the living space central to the plot, while also serving as a source of comedic relief through her teasing nature. Her key relationship is with her nephew Shintaro, whom she cares for despite her limited availability. Over the course of the series, her character does not undergo major dramatic change, but she is consistently portrayed as a supportive if somewhat mischievous presence in Shintaro's life. Her notable abilities include her skill as a published manga artist and her ability to maintain a successful career from a young age.