The most prominent feature of the *Yamawaro* is the belief in its seasonal migration with the *kappa*. In Higo (Kumamoto), it is said that the *garappa* (kappa) enters the mountains during the autumn equinox to become a *Yamawaro*, and returns to the river during the spring equinox to become a *garappa* once more^[2], rooting the concept that the water monster and the mountain monster are two aspects of the same entity. In the mountains, they help woodcutters carry timber in exchange for rice balls or sake, but it is said they will curse you if a promise is broken, or abandon the work if you are stingy with the rice balls.

In the Goto Islands, just as the *Wakan Sansai Zue* early recorded their habitation, the image of the *Yamawaro* as a mountain monster and the *kappa* (*gataro*) of the seaside and rivers have been spoken of as a continuum. The *Yamawaro* is said to let out a high-pitched whistle in the mountains, inviting people to sumo and stealing the vitality of the loser, but conversely, is also told of as a protector of mountain work^[3]. Its one-eyed, one-legged grotesque form is superimposed on the *Shansei* (mountain spirits) imported from China and the *Ippon-datara* of Kii and Shikoku, positioning it as a mountain monster of the western provinces in early modern natural history and yokai knowledge. The belief in the *Yamawaro*, which is two sides of the same coin with the *kappa*, reflects the mindset of people who feared the waterside and the mountains as a continuous sacred land.

Kunio Yanagita recorded this coming and going of *kappa* and *Yamawaro* in his *Santo Mintan-shu* (Collection of Mountain and Island Folktales) as the "Migration of the Kappa" [4]. It is considered a remnant of an ancient belief that the god of the river and the god of the mountain change their forms with the seasons. The *Yamawaro* is said to make a strange sound like falling trees (Tengu-daoshi), and mimic human singing or the sounds of work; there is also folklore that if you build a house on their path, they will get angry and poke holes in the walls. They are called by various regional names such as Yamanbo, Yamantaro, Seko, and Kashanbo, blending their image with other small mountain yokai.