A Taki Reio is a powerful entity found in Japanese Mythology and folkore (with further connections to Buddhist Mythology) that takes on the appearance of fearsome divine apparitions at the basins of holy waterfalls.
They mimic the form of other deities and are considered the apex of the supernatural world, with all other demons, spirits and yokai bowing before their might as embodiments of the gods themselves.
While often classified with yokai a Taki Reio is in reality a Kami (Japanese god), separate from yokai and other spirits, they are also a merging of Japanese mythology and Buddhist mythology as many of the figures they manifest as are both Japanese gods and Buddhist deities, this is due to a long history between the two cultures and the ability of Japanese folk religions and Shinto to merge aspects of other religions into itself.