Strongest Necromancer System - Chapter 35: All Night (+18)

“Missus, time to fulfil your duties!” Mu Yuchen demanded as he pulled Xi Xiaye closer with his arms intimately wrapped around her waist.

It was a meticulously planned feast for the powerful. Her fiancé had knelt down on one knee and proposed to her sister instead. Robbed of her right to her inheritance, she was prepared for the Xi family to throw her to the wolves.
As she slipped away from her family that had turned their backs on her, she found him — Mu Yuchen, the low-profile and reserved noble that ruled City Z and led Glory World Corporation.

“Mu Yuchen, let’s get married!” He looked up at her, then suddenly stood up.

“Where are you going?”

“Let’s go. Any later and the civil affairs bureau will be closed.”

- Description from Novelupdates

I reincarnated and became the young sect master of a sect that dominates a region.I originally thought that with my solid backing, I will not have any worries in this life. However, sudden changes occurred and the sect declined.When the last ten disciples were forced to leave, only a deaf old man and a dog named 'Haha' remained in the sect, I suddenly discovered that the buildings in the sect could be upgraded!I'll upgrade the main hall!I'll upgrade my residence!I'll even upgrade my kitchen!A super sect is currently rising inexorably like the Sun...Welcome to my sect.I only accept disciples that are geniuses. Even super experts have to pay if they want to join.There's no free lunch in the world!

Hitoshi's life sucked and then a truck made it even worse.But death wasn't the end. He wakes up in a fantasy world as a slave, expecting more of the same bad luck. Then a maid from the super-rich Aoi family buys him to work at their huge mansion. Finally, a break, right?Wrong.Sure, the mansion is amazing. The food is great. And yeah, the Aoi family treats him way better than he expected. But something's... off. Why do they watch him so closely? Why does everyone get weird when he smiles? And why do bad things keep happening to anyone who gets too friendly with him?Hitoshi just wants to be a good servant and make everyone happy. He doesn't realize that his kind heart and helpful nature are stirring up something dangerous within the Aoi household. In this new world, his greatest talent might become his biggest problem.They say no good deed goes unpunished. In the Aoi mansion, every act of kindness pulls him deeper into a web of obsession he never saw coming.“Reincarnated into Madness: Yandere Family's Unwanted Slave” is a story about second chances, magic, and what happens when being too nice leads to some seriously creepy consequences.

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