Mountain Sitting Immortal - Chapter 27: Mana Techniques.

A 30-year-old NEET is reincarnated into the body of an otaku that choked to death on instant noodles. As he comes to grips with his new life, he realizes that this world is subtly different from Earth. The denizens of this world are far better looking, and this new world also possesses futuristic technology as well as mysterious Yin Yang masters!

After a brutal day on the construction site,Jaxon collapsed onto his cot with nothing but sore muscles, a cheap dinner, and a phone in hand. Out of boredom, he picked up one of those mindless urban web novels—complete with arrogant young masters, all-powerful protagonists, and women falling in love every other chapter.“Who writes this garbage?” he muttered, tossing his phone aside and cursing the story, the characters, and the plot that made no damn sense.Then he woke up inside it.Not as the protagonist.Not even as comic relief.He’s the villain—the arrogant heir of a wealthy family destined to be publicly humiliated, slapped down by the protagonist over and over again.

I, Zatiel, Abyssal Lord, Ruler of Death and Destruction, Nightmare of Dys, have AWOKEN!!!!!.

His life contains events that can shake the universe:
-Fighting against Tiamat, Creator of Evil Dragonkind, in the first circle of hell, while billions of demons and devils butcher each other beneath them
-Start a World War against the Heavenly Race, and transform himself into a Golden Sun while he slaughters their greatest warriors, the Archangel.
-Enter the Final Gate and fight against the Outer Gods.
-Tearing the nine levels of Baator during his battles against the Prince of Evil, Asmodeus.

With his memories as a ruler of the Abyss and a Universal Existence, Zatiel will rise again.