I have Immortality In The Cultivation World - Chapter 599 - 438: The Substitute

Noah was a social outcast, bullied and shunned by his peers. He suffered humiliation after humiliation, building up a resentment for the world that he couldn’t act on, as he was as weak as they come.That is, until he discovers a dusty grimoire in his attic. Just by opening it, a mystical power flooded his very being, fundamentally altering his body and granting him a gift unlike any other.[Creator’s Grimoire System: Activated][Starting Level: 100]Equipped with the strongest system, unrivaled and seemingly boundless in its abilities, Noah decides to take back the life he missed out on, and much more.Weaving time, rewriting the memories of those around him, and even summoning fictional heroes, there seems to be no limit to the newfound power he has gained from his system.As the world’s first supervillain, he sets his sights on world domination, but who will try and stop the godlike youth in his path?

In the tenth year after the new era, the world finally came to an end. Zhang Mu truefully waited for his death, but unexpectedly found that he had returned to ten years ago. With his memory about the future, he swore that he would change the calamitous history, saving the earth from being destroyed! Walking dead, zergs, evolvers, and various mutated animals… nothing can stop him! The first step is to retrieve his identity as an era merchant , then find all the treasures he can remember to enhance himself!

- Description from Novelupdates

The first time they met they had battled fiercely, just for a mere bunch of herbs. She needed it to save people, and he wanted to use it to save his own life.

“Let go of it, or you will die.” The man’s violet eyes were cold and sinister as he said in a low voice.

She held on tightly to the base of the herb and pulled its roots right out of the ground, before she turned her eyes back with a crafty smile. “It’s mine now. Snatch it from me if you can.”

When they met several years later they were no longer on opposing sides in hostility. In order to repay the debt for having stolen the herb back then, she went on to miraculously cure his body’s condition, relieving him of the inhumane torment that wrecked at his body day and night. He was amazed by the godly skills in Medicine she possessed and his heart went on to fall irrecoverably head over heels in love.

- Description from novelupdates