I Became King Yama

A Ghostly Official, Literally a Real Ghost

Build the Underworld, Summon the Netherworld Officials, Command a Million Yin Soldiers

Not a bleeding heart, and actually smart.

Rebuilding Heaven or the Underworld with a System

The protagonist transmigrates to a world with neither a Heavenly Court nor an underworld. They get a System and gradually establish one of the two, eventually becoming its ruler.