Mikuni is an eight-year-old girl of aristocratic standing who resides within the sealed city of Atlas in the world of Shangri-La. She is often referred to by the titles The Moon and Digma 1, designating her as one of the candidate successors to the Atlas project. Her physical appearance is notably pale, a consequence of a collagen disease that prevents her from being exposed to sunlight. As a result, she spends her daily life sheltered from direct light, using a shade veil and traveling by a covered sedan when she must move outside her guarded palace.

Her personality is depicted as mysterious and distant, shaped by her sheltered existence and the power she wields. She possesses the uncanny ability to see through any lie spoken in her presence. When she detects deception, she responds with a brutal psychic power that contorts and crushes the body of the liar, often resulting in death. This ability gives her an aura of danger and reinforces her isolation, as few dare to approach her falsely. Despite her youth, she carries a sacred dagger identical to those held by Kuniko Hōjō and Kunihito Kusanagi, as well as an earring matching the one worn by Momoko, suggesting a hidden connection to these key figures.

In the anime adaptation, Mikuni is revealed to be a product of Himiko’s DNA, tying her origin directly to the central mystery of the story. Her role as a successor candidate places her at the heart of the conflict over control of Atlas, making her a target for various factions vying for power. Throughout the series, her interactions with characters such as Kuniko, Kunihito, and Momoko gradually expand beyond her guarded existence. Her development sees her moving from a secluded, almost puppet-like figure to one who seeks refuge in Akihabara, allowing for tentative steps toward greater openness and connection with others. Her notable abilities—lie detection and lethal psychic manipulation—make her both a formidable and tragic figure, as her power isolates her as much as it protects her.