Annin serves as the guardian of the Furnace of Eight Divisions, the magical barrier that separates the living world from the Other World. She's one of the rare beings under King Yemma's authority who doesn't resemble an ogre—she actually looks human, despite being immortal and ageless.
She's held her position as the sole keeper of the Furnace for over ten thousand years, which makes her genuinely ancient even though she maintains a youthful, attractive appearance. The Furnace itself exists for a critical reason: those flames prevent demons and other creatures from the Other World from escaping into the land of the living. If they're extinguished, even momentarily, everything gets through.
When Goku shows up asking her to put out the fires ravaging Fire Mountain—which is threatening to destroy the Ox-King and his village—Annin flatly refuses. Goku keeps pushing, and the two end up fighting over it. During the scuffle, Goku accidentally discovers just how old she really is and, being Goku, kind of laughs about it. Annin doesn't take that well. Furious, she transforms into a giant and starts trying to crush him, using her headpieces like weapons and creating wind gusts with her cape.
Goku manages to hold his own thanks to the Bansho Fan, which surprises Annin with its sheer power. Realizing she won't win this way, Annin offers a compromise: she guides Goku through the Furnace flames themselves so he can extinguish the fire from the other side and save the village without actually breaking the barrier. After that, she disappears from the series entirely.
Content compiled by AnimeList.moe from publicly available sources.
