The strongest demon there was, the pinnacle of all beasts..

The axe demon, Onokuma.

He was undefeated, and reigned for over two centuries.. Until, after reaching the level of 650, he found himself with no joy in the world. No one neared his power, which meant no one could defy him.

What was once a dream, turned into a nightmare. He longed for stronger opponents, and asked the gods to help him.
...
"Where am I..? Most importantly..."

"Whose body am I in?"