A Japanese [Shinto Buddhism] practice of ritual purification by washing the entire body.
This is usually done on a waterfall with very cold water. The cold water is said to “shock” any negative energies, demons or spirits out of ones body.
In traditional hydrotherapy it is best to alternate between hot and cold water and always ending with a cold rinse. This is due to the fact that the heat causes increased blood flow, inflammation and vasodialation (which is not good for the body in the long term) and cold water causes vasoconstriction which lessens inflammation and swelling (which is physically optimal). Btw, this is ACTUAL medical advice NOT magickal advice. Do what you will, I’m just being informative.