The Yamabiko, “mountain echo” or simply “echo” is heard rather than seen. It is found in the high mountains of Japan, and answers anyone shouting in the mountains with a mocking echo of their voice. While there is no definite version of its appearance, it was depicted by Toriyama Sekien as a rather simian creature.
Its name can also be interpreted as “spirit of valley reverberation”. It is not known if the yamabiko yokai was named for the echo, or if the echo was named for the yokai. The Yamabiko Shinkansen train, on the other hand, is named for the echo and not the yokai.
Foster, M. D. (2015) The Book of Yokai. University of California Press, Berkeley.