Paladin of the Spirit by Marvin Knight

In the depths of Hell, Darren grew strong. Now he's ready to return as he prepares to face down the man who killed his mother.
The world thinks Darren is dead. Now is the perfect time for him to build his strength and prepare to wage war on the heavens themselves. To prepare to attack the heavens, he will destroy the hells.
With an army of loyal holy warriors at his back, Darren is prepared to return to Limedeep, and then head into the fiery depths that forged him into the unstoppable warrior he became as a man. With him to lead them, all of his followers will undergo a baptism of fire and death, rebuilding them into human warriors of a caliber never seen before in the Sacred Seas.

Contains: Gamelit system, multiple love interests, and one badass paladin.