A school of koi reached a waterfall at the end of the river, many of the koi turned back, letting the flow of the river carry them away. The remaining koi refused to give up. Leaping from the depths of the river, they attempted to reach the top of the waterfall to no avail.
Their efforts caught the attention of local demons, who mocked their efforts and heightened the waterfall out of malice. After a hundred years of jumping, one koi finally reached the top of the waterfall.