Mizuchi

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.

In olden times pronounced mi-tsu-chi, the word can be broken down to mi "water" + tsu a particle meaning "of" + chi "spirit".

Under the 67th year of the reign of Emperor Nintoku (conventionally dated 379 AD), it is mentioned that in central Kibi Province, at a fork on Kawashima River (川嶋河, old name of Takahashi River in Okayama Prefecture), a great water serpent or dragon (大虬) dwelt and would breathe or spew out its venom, poisoning and killing many passersby.

He approached the pool of the river, cast three calabashes which floated to the surface of the water and challenged the beast to make these gourds sink, threatening to slay it should it fail.

[c] One of the men, who resisted being sacrificed, employed the floating calabash and dared the River God to sink it as proof to show it was truly divine will that demanded him as sacrifice.

The tanka poem #3833 composed by Prince Sakaibe [ja][16] can be loosely paraphrased to mean "I could ride a tiger to leap over the Old Shack, to the green pool, to take down the mizuchi dragon there, if only I had a sword capable of doing just that".

This is because the kappa creatures are known locally by many names that sound much like mizuchi, such as mizushi (former Noto Province, Ishikawa Prefecture), medochi (Nanbu region, parts of Iwate, Aomori, Akita), mintsuchi (Ezo, now Hokkaido).