There are mysterious creatures in Japan called Oni.
In general, they are thought of as guards of Hell, but they are also living manifestations of various emotions of the unfortunate, such as jealousy, vengeance, and sorrow.
Or the fear and prejudice against strangers manifested as monsters.
They are a little different from the devil and demons of the West.

Oni are the unique product of Japan's spiritual culture.
For the Japanese, Oni are both mysterious monsters and lovable creatures. Here are a few of the many expressions which use the word "Oni":

Oni-musha (Oni-warrior): A ruthless warrior or brave person
Oni-baba (Oni-old woman):A mean woman
Oni-kohchi (Oni-coach):A very strict coach [of athletic teams, etc.]
Tears in the eyes of an Oni:Even the meanest person has feelings
An Oni with an iron club:Invincible

Doing the wash while the Oni is gone: Similar to the English expression "When the cat is away the mice will play."

The relationship between humankind, Kami, and Oni, is like a three-way battle.
They form a circle, which cannot be broken, that spins around and around inside people's minds.

The Oni that bring happiness to humankind are called Kami.
The Kami who curse and torment humankind are called Oni.

The mind which brings happiness to humankind is called Kami.
The mind which curses and torments humankind is called Oni.

A never ending Oni game.

Who is it that stands behind you now?