MTL - Grasping Evil - Chapter 1245 Saints

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

They are childhood sweethearts, they are engaged under the family’s scheme, and they have to live in the same room and sleep together.

That night, she was accidentally drunk, and he kissed her in a fascinating mood,. By accident, his “crime” was finally discovered, she accused him, but he said with a smile, “You are my wife, why can’t I kiss you?”

The two people’s daily routine is full of bickering, mutual hate.

He said that he disliked her. Actually, In his heart, he was extremely caring of her. When she was close to other boys, he was so jealous that he wants to tie her to his side and become exclusively his.

"Marry me. Once we're married, I will be loyal to you for life—as long as you keep me alive." Qiao Jiusheng was pushed into the water by her older twin sister, had her identity stolen, losing her old love and life. With no other choice, she seeks out Fang Yusheng, the blind man rumored to have no interest in women. With blank and empty eyes, he says, "Sure." In her past life, she was betrayed by her sister and trapped in the basement. Her tongue was cut off as she watched her sister take her place, winning overall her loved ones, marrying her lover of six years, and starting a family with him. Now that she's back to a time before it all went wrong, Qiao Jiusheng escapes from the river and goes to her boyfriend's older half-brother. She puts on a mask and marries him, to fight their common enemy. The wheels of fate begin to spin, and the severed threads of destiny are once again entwined... Before their wedding, he tells her, "Don't peek at me so openly just because I'm blind and can't see you." On the night of their wedding, he tells her," You don't have to dress like a bear. I don't care for women." Half a year after their wedding, just because she gives another man another look, Fang Yusheng covers her laptop, phone, bedside drawers, desk, and wallet with nothing but his selfies.

The strongest Demon Lord dies, and reincarnates as a human. Not only that, he because of various incidents turns into the hero’s best friend.

Follow his journey as he tries to help the hero escape his fate, and on the sideline to conquer the continent while he’s at it.