One Piece: New Order - Chapter 93: Rosinante

“I'm a monster? Why is every player I see trying to kill me?”------------Kai, a young man paralyzed by an incurable disease, decides to play the new VRMMORPG called Realms of Monsters in search of freedom and adventure. However, when he logs in for the first time, something unexpected happens.While everyone else chooses their class and race, Kai awakens in the middle of a forest... as a salamander.Luckily for him, he won't stay a salamander for long.[Mythical Evolution System activated.][Devour a monster to evolve.]Trapped in a monstrous form, Kai must navigate a hostile world where every player is a potential enemy. With the Mythical Evolution System, his survival hinges on his ability to evolve and grow stronger. In a game where everyone else is a hunter, can Kai rise from being the hunted to becoming the ultimate predator?

In novels with a stud there is always a Senior Martial Brother like this:

In the early stages of the novel, his innate talent is high, his cultivation is good, his appearance is handsome, and he has an intelligent, cute younger Martial Sister as a fiancée.

In the middle stages of the novel, he is caught unprepared and defeated by a young disciple (the protagonist) in the sect who’s hardly remarkable at all. From then on, he falls from his godly altar and loses his brilliance. Even his young Martial Sister leaves him for someone else.

In the late stages of the novel, he continues to turn dark, going down the Demonic Path and becoming the major villainous boss. However, the protagonist still ruthlessly defeats him and his soul is eternally sealed.

Once Qin Mo opened his eyes, he discovered that he had become this Senior Martial Brother.

- Description from Novelupdates

Gu Shanhai witnessed this great world of numerous heavens and discarded his third life.The gods of the human realm forged an eternal utopia with blood and fire.The King of the Red Dragon led his knights, patrolling the never-setting empire.The scholar, with a smile and a sword stroke, depicted thousands of miles of rivers and mountains, while monsters opened their eyes and stretched forth claws, giving birth to all manners of demons....'Everyone here is a player; you can't call me abnormal just because I haven't been digitized, right?'

[R18 novel with a lot of sexual content]Artem never expected to take on the role of a villain, let alone transmigrate between harem novels. Bound by a system, his task is clear: steal the heroines from all the protagonists’. From Chinese Cultivation and Korean Gate to Japanese Isekai Fantasy, VRMMORPG, and beyond—no heroine is off-limits, and no protagonist is safe!