"Master of Mosquiton" is a six-episode OVA series that blends supernatural horror, comedy, and action. The story is set in the 1920s and revolves around Inaho, a high school girl who stumbles upon an ancient artifact while exploring a mysterious mansion. Upon touching the artifact, she inadvertently awakens Mosquiton, a centuries-old vampire who has been sealed away. Mosquiton, who claims to be the "strongest vampire in the world," is bound to Inaho due to her bloodline, which connects her to the artifact. The two form an uneasy alliance as they embark on a quest to locate the "O-Part," a legendary treasure said to grant immortality.

The narrative unfolds as Inaho and Mosquiton are pursued by various factions, including the Vatican's secret organization, which seeks to eliminate vampires, and other supernatural entities vying for the O-Part. Along the way, they encounter a diverse cast of characters, such as Karen, a vampire hunter with a tragic past, and Ban, a rogue vampire who becomes both an ally and a rival. The series explores themes of immortality, loyalty, and the consequences of wielding power, as the characters navigate a world filled with danger and intrigue.

The dynamic between Inaho and Mosquiton serves as the core of the story, with Inaho's resourcefulness and determination contrasting Mosquiton's arrogance and supernatural abilities. Their journey is marked by episodic encounters with enemies and allies, each contributing to the overarching plot of the O-Part's discovery. The series balances action-packed sequences with moments of humor and character development, creating a fast-paced yet engaging narrative. While the story concludes with the resolution of the O-Part arc, it leaves room for further exploration of the characters' relationships and the broader supernatural world.