Chiharu, a genetically enhanced human designated as a "super human," exhibits extraordinary physical and cognitive capabilities surpassing ordinary limits. After a reckless high-speed incident on the Milky☆Highway, she and her cyborg partner, Makina, faced arrest for breaching Galactic Traffic Laws, culminating in a court-mandated sentence to clean the Milky☆Subway—a sprawling interplanetary railway linking distant worlds.

Her past reveals a penchant for impulsive decisions, frequently pursuing thrill-seeking escapades alongside Makina, regardless of risks. Their cleaning duty takes an abrupt turn when the dormant subway mysteriously activates, hurtling into space. Trapped aboard, Chiharu must confront escalating chaos within the claustrophobic confines of the train, starkly contrasting her typical unfettered mobility.

Chiharu and Makina’s partnership thrives on improvisational teamwork, marked by rapid-fire banter that spins precarious scenarios into comedic chaos. Their dynamic leans into humor-driven, unconventional problem-solving, amplifying both tension and levity. Visually, Chiharu’s exaggerated, dynamic expressions mirror the series’ frenetic comedic rhythm and bold aesthetic, reinforcing its stylized storytelling approach.