Answer:
A trout.
Step-by-step explanation:
Before the creation, if we believe the Ainu legend, there was a swamp. In that swamp was a large trout the Creator used as the foundation of the Earth.
Its existence at the base of the Earth helps explain the natural disasters the people of Japan have to deal with - it produces tidal waves and earthquakes.
This trout was such a powerful fish the Creator had to make two gods stand by its side to keep it quiet. The legend says they needed to always keep one of their hands on it in order to keep it calm.