Ichiban Ushiro no Daimaou - Volume 7, Chapter 3 — The Demon King and the Whereabouts of the Holy Grail

Jin Runcandel is the youngest son of the greatest Swordmaster. After he gets himself kicked out of their clan, he meets a tragic fate…but before he dies, a God gives him a second chance. Now he must use his new power for good.

To reward Meng Fan for his bravery before his heroic death, the cosmos rewarded him with a ‘system’, sending him back in time to three months ago, alive.

He had never invested in shares or bought a lottery ticket, and neither did he have any experience in the general business industry. Lu Li found that the only thing he could do was play games.

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