Mizuchi

Agatamori battling mizuchi in the pool. From Zenken kojitsu (1878)

The Mizuchi (大虬, 蛟龍, 蛟, 美都知) is a type of Japanese dragon or legendary serpent-like creature, either found in an aquatic habitat or otherwise connected to water. Some commentators perceived it to have been a water deity. It is described in the Nihon Shoki and one Man'yōshū poem.