Isai is Kourin's nyokai and serves as one of Kourin's shirei. She only appears in the anime.

Isai's appearance is an anthropomorphic creature covered entirely in fur and possessing red-tipped feathery wings. Her hands and legs are like a leopard, and she has spots on her paws, legs, and tail. Her feet have talons like a bird, though they are also covered in fur.

(Source: wikia)