Nyantenshi is a white male angel cat banished from heaven for undisclosed reasons, his personality hinting at misbehavior as the cause. Cast out, he now wanders Earth as a fallen angel. His appearance features white fur, black eyes, and distinctive black feathered wings that remain unnaturally stationary even in flight. A recurring character tic sees him often posing with a smug expression and his right hand held near his mouth.

He exhibits a trickster personality, fabricating stories about his banishment which he later casually admits are false. His manipulative antics frequently involve chasing the smaller cat Katsuo to steal items like sardines or lollipops. Nyantenshi maintains a perpetual smile and an aura of dissonant serenity, rarely displaying overt emotion compared to others. He employs deadpan snarking and deliberately provokes reactions, such as mocking Nyanpire's illness while reminding him of his vampiric immortality.

His interactions underscore his opportunistic nature. He allows Nyanpire to drink his blood without consequence, leveraging his own immortality specifically to annoy the samurai cat Masamunya. Nyantenshi's presence often incites jealousy in Masamunya, particularly during moments focused on Nyanpire. Expressing contentment with his existence on Earth, Nyantenshi views his banishment as freedom to act exactly as he pleases.