- "I found it at the end of an animal track, where the spirit peaks of the north rise in ranges. A temple, long abandoned by its god. The woods and the spirits who dwelt within it gathered to me. For centuries I lived... unseen by human eye. But now you've found me. You are a man of means, I see."
- — Isabi
Isabi, also known as the King of the Mountain, is a Forbidden Magic Law practitioner, who turned himself into an envoy to gain eternal life. He is at least 2000 years old.
Isabi became an envoy, seeking immortality. In his younger days, he knew Teeki, whom he claims was a "trouble-maker", doing things like making Mt. Fuji erupt, releasing 100,000 evil spirits on Kyoto, and making the entire Taira army disappear. He also fought Teeki on occasion, and was evenly-matched. He also held the Writ of Passage to the endless abyss, a powerful artifact, which he kept at the bottom of his sake bowl (he eventually hid the Writ at the Magic Law Association). Isabi also was a member of Ark, until he left, seeking peace and freedom. Page and Yoichi came to ask Isabi's help in defeating Teeki. Isabi assaulted them when he found out that Yoichi sealed several of his Mountain Spirits in stone. They ended up on top of Isabi's castle, facing off. Page rang the Bells of Troy and summoned the Smithy of Hades. After a long battle, Isabi was defeated and Page was left on the brink of death. Isabi quickly recovered, offering to heal Page, since he was the first man to beat him. Isabi told them that even though he was evenly matched with Teeki long ago, that is not the case now. He tells them that they need the Writ of Passage in order to defeat Teeki, which is hidden at the Magic Law School (initially, he has trouble remembering the location of the Writ, due to drinking too much sake).
Isabi is an envoy, so he has access to many spiritual powers. He can fire a spear of lightning from his horns, and can grow to large sizes. He can also heal himself, which causes mushrooms to grow on his body. He also can use this method to heal others, which he uses on Page after their battle.