Demon Queen Rebirth: I Reincarnated as a Living Armor?! - Chapter 7 - A Living Armor’s Strongest Cheat Is...

Li Xuehao found a secret of monasticism in the cover of the genealogy. After spending ten years, he finally succeeded in building the foundation. Unexpectedly, he was eager to get rid of the evil spirits. After his death, he was born again in Yokohama, Japan, and was attached to Sakura, Tsurumi. The story of the high school student Gao Zhonghao in the college, the story begins here…

- Description from Shubaow (Translated)

He is a young man without a spirit root. It is believed that this denies him the chance at cultivation. However, a mysterious lady imparts a Supreme Demon Classic to him and from then on, he starts his path of cultivation.
He undergoes a total transformation to emerge as the most fearsome and powerful fiendish demon in his era, that even immortals and fiends are fearful of him, and saints are at his beck and call.
Mastering the Supreme Demon Classic is the turning point in his life. He is able to unleash his immense and divine power from within, illuminating the entire universe!

- Description from Novelupdates

I became a side-character who died in anguish because of her good-for-nothing husband.

If I can’t avoid getting married, why don’t I change who I marry instead?

“Excellent, marriage sounds good.”

“Wise choice. Then let’s have a wedding ceremony that isn’t too ceremonious. Following that, I’ll need you to go down to the Fief and behave like the lady of the house until I call for you. Naturally, there won’t be any time to spend in leisure whilst dousing yourself in luxuries.”

“I’m not marrying you, but your father instead.”

“……Pardon?”

“I’m not going to marry you. Do you have a problem with that?”