The Arrogant Immortal - Chapter 24 - Sister Please Be Reasonable

A skilled but unfortunate modern-day assassin was killed in a freak accident. However, he soon found himself summoned to another world by an evil wizard, who had him possess the body of a boy as an experiment. After successfully planning the evil wizard’s downfall, he used the wizard’s body as a springboard to gain influence and power in his new world.

- Description from Novelupdates

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

Michael Alastair never mattered. In a world where strength was everything, he was nothing—just another powerless kid, easy to break and easier to forget. When his tormentors finally took things too far, his story should have ended in that alley, bleeding and alone.But fate had other plans.In the void between life and death, a voice spoke. Cold. Sharp. Amused. [NEW TALENT UNLOCKED: WRITER’S LEGACY]. A system unlike any other—sarcastic, relentless, and strangely invested—offered Michael a power beyond reason and a purpose he never imagined. Now, armed with an SSS-rank ability and a mission to rise, he’s back. And this time, he won’t just survive—he’ll rewrite the rules.