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Isai (尹灑) 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.

As Kourin continues to obey King Kou's orders, her shirei are gradually reduced until only Isai and Gajyou are left. When Kourin sacrifices herself to prevent King Kou from killing Youko Nakajima, Isai appears and embraces Kourin and takes her body away as she dies.