Nyanpire began as an abandoned kitten near death, rescued and granted eternal life by a passing vampire who shared his blood. This transformation turned the kitten into a vampire cat, emerging with distinct physical traits: bat wings and a yellow cross marking on his stomach.

He lives primarily as a domestic house cat with his human owner, Misaki. His daily existence blends typical feline behaviors like chasing yarn or basking in sunlight with vampiric needs; he actively seeks blood for sustenance but shows a strong preference for red alternatives like tomato ketchup and blood orange juice. His personality mixes curiosity and excitability, often reacting with high energy to new situations. He values reliability, especially in his self-perceived role protecting other household cats, yet experiences anxiety when separated from companions or facing disapproval.

Relationships define much of his life. He shares his home with another cat, Chachamaru, and forms bonds with neighborhood cats including Masamunya, a samurai cat who develops romantic feelings for him, and Nyatenshi, a mischievous angel cat banished from heaven. Two bats, Mori and Komori, periodically appear, implying a loose connection to his vampire creator.

His vampiric hunger surfaces in the recurring phrase "Give Meow Blood!" While generally embracing his vampire abilities, he occasionally overlooks aspects of his immortality, needing reminders about his invulnerability to common ailments.

Nyanpire confronts the emotional weight of his eternal existence, grappling with the realization that he will outlive his human owner, feline companions, and friends. This leads to feelings of loneliness and concern about his future, highlighting a tension between his playful daily life and the deeper implications of his vampiric nature.