Mariko is one of the supporting characters in the series. She is an adult woman with long pink hair and red eyes. Her background places her as a member of the Japan Self-Defense Forces, and she is stationed in Hokkaido. Mariko is a highly skilled marksman and relies on firearms as her primary means of engaging supernatural threats. She also possesses the unique ability to sense the presence of yokai, making her a valuable asset to the group of friends she encounters.

In terms of personality, Mariko initially comes across as stoic, reserved, and reluctant to show emotion or discuss her past. She rarely opens up about her history and tends to keep a professional distance. However, beneath this composed exterior, she has a kind and caring nature. She is warm-hearted and often takes on the role of an older sister figure, looking out for those around her and offering support when needed. Her past experiences have instilled in her a strong determination to protect the people she cares about, even at the risk of her own safety.

Mariko serves as a supporting figure in the story, providing combat expertise and guidance during encounters with yokai and other supernatural phenomena. Her abilities allow her to perceive threats that ordinary humans cannot, aiding the main characters in navigating the dangers of their world. Over the course of the series, Mariko gradually grows more comfortable with her companions, revealing her vulnerable side and deepening her bonds with them. Her development involves learning to trust others and allowing herself to be part of a community beyond her military duties. Notable abilities include her sharpshooting skills, her innate sensitivity to yokai, and her experience as a member of the Self-Defense Forces, which gives her a tactical mindset and a sense of discipline.