Mutsuki Nenga is a young female officer serving in the Galactic Patrol, the intergalactic law enforcement organization that pursues the space pirate Mito. She is the older sister of Masatsuki Nenga, and the two siblings work together in their quest to capture Mito and her crew. Mutsuki is characterized by a strong sense of duty and dedication to her mission, but her effectiveness is frequently hampered by a unusual biological condition: she forgets to take her medicine, which is necessary to suppress a fungus that grows on her scalp. This recurring personal struggle adds a layer of comedic difficulty to her otherwise serious role as a patrol officer. Her alien biology is also notable for being nitrogen-based, making direct exposure to water lethal for her. As the series progresses, Mutsuki develops romantic feelings for Aoi Mitsukuni, the son of Mito, creating a significant internal conflict between her professional obligation to arrest his mother and her growing personal attachment to him. This emotional tension becomes a key part of her character arc, as she must navigate the line between her duty as a patrol officer and her evolving connections to the people she is supposed to bring to justice. Her relationship with her younger brother Masatsuki, who is more overconfident and eager to capture Mito to restore their father's honor, further defines her role as a more grounded and cautious counterpart within their family dynamic.