Ippon-datara is a mountain yokai with one thick, trunk-like leg and a single saucer-sized eye. It is especially well known in the Kumano mountains along the border of Wakayama and Nara — the old provinces of Kii and Yamato.
Its name is linked to tatara iron-smelting, worked with bellows, and one theory derives it from a one-eyed, one-legged blacksmith. It is normally shy, hopping away at the sight of a person, but once a year, on December 20th, it turns violent and crushes anyone it meets.