Chaos Warlord: Reincarnated in Eldrich with the Devil System! - Chapter 81 : The Imposter!

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

[R-18, Mature Element Warning!] [Multiverse!]A young man with a questionable job dies, eaten by a shark. To his surprise, afterlife was a spinning roulette that decided his next world and powers, with an annoyed Goddess supervising the process.The Gamer System welcomes him with open arms, and he shivers in the endless potential it holds. If used right, he knew The Gamer could step beyond even Godhood. Beyond God.Out of desperation, that was exactly what his goal became. The Goddess was a snitch, and now she and her fellow Gods wanted him dead. What, and why?In the end, [Soul 799], soon to be renamed as [Neji Hado], becomes a Cursed Soul.-—-Tags: Gamer-System, Gray-MC, Harem, Incest, Mature, Multiverse, R-18, OP-MC, World-Hopping.First World: My Hero AcademiaSecond World: NarutoThird World: Fate/Grand OrderFourth World: High School DxD

The story follows Danheng, who transmigrates to the Douluo Continent seeking a peaceful life, only to be persistently pursued by Gu Yuena, who insists on becoming his wife. She encourages him to strive for greatness, aiming for him to become the leader of soul beasts, the Dragon God, and the ruler of the Divine Realm. Despite his desire for a quiet life as a librarian, Danheng finds himself entangled in various challenges due to his wife's ambitions.

A river song, triggered a legend of the rivers and lakes.
Tian Zun’s life motto: “My sword is the truth.”
Shen Lang’s life motto: “To serve people with morality, those who are dissatisfied are dead.”

- Description from uukanshu (translated)