Moku-gyou lives in the Tree of Life, Mingke-shu, in Ming-ken.
When the player is Tou, Moku-gyou gives them the mission to go find the names of each of the Zoh-gaeru family's members, and input them into the computer in the Computer Room of Tong-tah, Thi-eng, as well as Tou's own name.
When the player is Byou, they must pick up Retsu and feed it to Moku-gyou to gain access into his mouth. Inside of Moku-gyou's mouth, Moku-gyou asks Byou who the eyeball inside belonged to. When the player answers "Tou-gyou" they receive the eyeball.
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This article contains important plot details.
At the end of the game, Tou-gyou reveals that with the other three kings, Moku-gyou overthrew him, cut him up into eight pieces, and scattered the pieces throughout the land after they found out about the use of human souls.