はくだのつまどい

What Kinu, a girl who woke up in the dim room found was a letter.

[The mountain god disguises as a human and knock on the door. It is said that the true form is somewhat strange-looking. Once you provoke the mountain god, the river will be swallowed, the mountain will be destroyed, the sky will be concealed, by the act of the mountain god. Never, ever make the mountain god angry.]

….Then there was a sound of knocking on the door.