From Ainu Folklore
This world is, under the Creator of all things, governed by the Goddess of Fire as his deputy. Originally this goddess had her home in heaven above, but was sent down by the Creator to take care of the world. Having heard that it was determined that she should leave her heavenly home and descend to earth, the serpent, being enamoured of her, desired to come down in her company. Having expressed his ardent love, the goddess trying to dissuade him from this course, informed him that if he descended with her he would be obliged to endure fire, which would be exceedingly hard for him. Notwithstanding all this, however, he declared himself ready to brave everything, if only he should be permitted to accompany her. And so, after having received full permission, he came down with her in a flash of lightning. Here he has been every since, and here he is to remain.
The serpent, descending as he did in the lightning, came down with such mighty force that his fall made a large hole in the ground. Even at this present day some of his offspring who were left behind in heaven, and have a longing to visit their father, likewise descend in lightning, and the force of their fall also makes holes in the ground. These holes, when known to exist, should by no means be approached, for they lead down to Hades, which is now believed to be the true home of the serpent kind. The original father-snake has his place there, and there reigns as king over all his tribe.
Source:
The Ainu and Their Folk-Lore, John Batchelor, 1901
Kotharian Lightning 