Heavenly Demon Reborn! Vol 2 - O'Emperor - Bog

Reborn as the lowliest member of the Heavenly Demon cult, Unseong embraces the ancient techniques and secrets they teach him to increase his abilities. Rising from the most likely to die in training to the leader of an elite squad, the members of the cult find that Unseong far surpasses anyone's expectations, challenging even the cult's leaders' levels of power. And while he plans to use those powers to avenge his murdered master, Unseong may not be able to protect himself from the dangers of the demonic arts.