Elf Tensei Kara no Cheat Kenkoku-ki - Chapter 3Book 1: -1: Two Promises

Escaping from the wedding she dreaded with Crown Prince, Aed Ruad, Princess Anastasia ended up becoming the captive of the Lore's most dangerous man, Prince Ileus.

A loner boy, who’s always loved escaping into his RPG world, suddenly finds himself living as one of his game characters. But instead of becoming his favored fighter, he’s in the body of his second avatar—a support mage! Though he’s used to playing both roles, being the mage in real life is a whole new challenge. Now he must rely on his knowledge and skills to navigate this unfamiliar reality and survive as the game's “support.”

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

To [Player]: This is the mystery of life and the journey of all things.

You will be stronger, become superheroes, and even touch the power of gods. But if it fails, it is death.

Because you have embarked on the evolutionary game of the highest sequence!

“Isn’t this just embarrassing Darwin?” Li Changhe murmured as he looked at the [player] who came from a distance: “It also embarrassed Newton by the way.”

Don’t spray if you don’t like hot blood

- Description from novelbuddy