Mutsuki Nenga operates as a Galactic Patrol officer focused on capturing space pirate Mito. As a nitrogen-breathing alien, exposure to water inflicts lethal physical damage and psychological trauma on her. This biological weakness demands consistent medication to prevent stress-induced fungal growth on her scalp. She partners with her younger brother Masatsuki Nenga in their shared mission to reclaim their family’s honor, tarnished by their father’s disgrace within the Galactic Patrol.

Initially embedded undercover as a transfer student at Aoi Mitsukuni’s school to surveil Mito, she unexpectedly develops romantic feelings for Aoi—the son of her primary target. After Aoi transitions into a female and rises as galactic queen, Mutsuki shifts roles to serve as her personal bodyguard and romantic partner. Their bond deepens amid Aoi’s royal duties and the resurgence of Hikari, the galaxy’s original queen.

When possessed by Hikari, Mutsuki endures the entity’s exploitation of her body to undermine Aoi’s reign. Following her liberation from this control, she persists in safeguarding Queen Aoi while untangling their intricate relationship. Her character balances intense emotional outbursts—often tied to her species’ vulnerabilities—with unwavering dedication to her duties across galactic strife and personal turmoil.