Playing Waterbending (Avatar: Last Aibender SI) - Chapter 30 -

An RPG gamer who played the realistic VRMMORPG ‘The Amber Sword’ for years, finds himself teleported to a parallel world that resembled the game greatly. He takes on the body of an NPC who was fated to die, and with the feelings of the dying NPC and his own heartrending events in the game, he sets out to change the fate of a kingdom that was doomed to tragedy.

- Description from novelupdates

This legend tells the tale of the protagonist, Kuroki summoned to protect the demon king from the hero.

Kuroki, unbeknownst to him, suddenly came to another world. He was summoned by the demon king, Modes. The territory which the demon king overrules was in the midst of being destroyed because of the hero. He had no choice but to bow before Kuroki.

“Please save us, Savior Dono!”

Kuroki nodded, deciding to save the demon king due to an unexpected turn of event.

The end of the world is coming, the world has undergone great changes, and everything has changed. Plants, animals, and even insects, as long as there are living things, have mutated.
Become more powerful, and even evolved supernatural abilities, such as chickens and ducks that can fly to the sky, such as cats and dogs that can breathe fire.
But only humans, without any obvious changes, seem to have fallen from the top of the food chain to the bottom of the food chain overnight.
Any creature that can open its mouth to eat can treat humans as food.
But fortunately, this world has not completely killed humans. Gradually, humans discovered that they had the ability to cultivate compatibility with other creatures.
As long as it has a high degree of compatibility with some powerful mutant creatures, it can be used for its own use to achieve the purpose of protecting itself.
Fang He is a person who is very compatible with mutant animals, but it is also because of his ability that he has changed from the strongest to the stupidest.
Fang He, who was reborn, said, “Hmph, this time…”

- Description from novelbuddy

Long Chen, a crippled youth who cannot cultivate, is constantly targeted and bullied by his fellow noble heirs. After a particularly vicious beating, he wakes up and realizes a Pill God’s soul has somehow merged with him, giving him some additional memories. Within those memories is the mysterious Nine Star Hegemon Body Art, a cultivation technique that even he can train in, but whose secrets and origin are still a mystery to him. Relying on his improved instincts as he finally begins to cultivate, he realizes a huge conspiracy is underfoot within the Phoenix Cry Empire, one involving his father, members of the imperial family, and even the Emperor himself.

In order to solve the mysteries around him, he must rely on his new alchemy techniques and the powerful but baffling Nine Star Hegemon Body Art. Countless enemies block him as he attempts to climb to the peak of the cultivation world.

Fate destined him to be only a chess piece, but he would not bow to the will of the Heavens.