In the war between the nine realms, the demon king was killed. Accidentally reborn in the human world three thousand years ago, he remembered his failure three thousand years later, learned his lesson, and began to develop his own power in the human world. Finally, he returned to the demon world, leading both the human and demon worlds to fight back to the divine world and dominate the nine realms.
Can't you use your brain more?
It's over. It's inexplicable.