1 King Among Kings

There are 7 Demon Kings and the 7th King was the strongest.

He was feared by all the kings and the world but one day the 7th king disappear.

He was forgotten buy the world and the king, after 350 year have passed the 7th king reappeard ones again.

But he was reborn as a kid, his memory was erase but not all just 2 or 3.