All the Heroines are my Ex-girlfriends - Chapter 164 - : Izumi Sagiri and Izumi-mama

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

Nessa was transported into a new and completely unfamiliar world where monsters roamed free and survival of the fittest was the supreme rule for the majority of them. In this world, which was beautiful yet dark and cruel, she was given an opportunity.An opportunity to build her own nation after becoming the leader of a few peculiar monsters.Will she be able to overcome those who oppose her, threaten what she is creating, and demonstrate her power to the world in order to achieve peace and acceptance, or will her efforts in this world be futile?[System notifies]Come join Nessa and a few kind souls on their journey to create a nation where monsters, humans, and other creatures can coexist and live happily.

Leon, a man who tragically died of exhaustion due to his sister's otome game, unexpectedly finds himself reincarnated as a young aristocrat named Leon Bartfort. However, he soon realizes that he is not alone in this body. Another mysterious entity already resides there, its voice echoing in his mind.Who is this second consciousness? Is it a friend, an enemy, or something far more sinister? Will they be able to come to an agreement to share control over the body, or will a fierce struggle for dominance ensue? Or perhaps their interactions will lead to unforeseen consequences?Intrigued? Then start reading!

I finally managed to kill the demon lord.