MTL - Marvel: Start with Summoning the Shadow Troopers - Chapter 36

Being the author of the breakout novel, Gates of The Primordials, Jarren Fletcher did not care about the constant critiques claiming he had a habit of treating extra characters as mere plot devices, creating and then dumping them once they’d served their purpose.To Jarren, it didn’t matter. Extras were just that—extras. All that mattered was the main character.But Jarren never expected to wake up in his own story, reincarnated as one of the meaningless, disposable extra characters, Deremiah Morcant—a coward who took his own life to escape the perilous challenges of the Gate Trials.Now, Jarren has to face those deadly challenges himself in the body of a weak, insignificant extra. He must find a way to survive in the rules of the dangerous world he had created, whilst also trying to save it.But time is running out. The next Wave is coming, and so are the paragons.

A tree of 10,000 flowers, the world is the door.
The spells change a lot, but the hearts of the people are unchanged.

- Description from Uukanshu translation

Su Yun was a prodigy, blessed by the gods. However, life is never so easy. Soon after reaching 6th stage in spirit novice realm cultivation, his progress stagnated due to incurring a rare medical condition.

A few years go by, and Su Yun has spent all his time gambling or drinking, wasting his youth away, but one day everything changes. Qing Er, the only one who stood by him was forced by his clan to be a sacrificial bride to someone she didn’t love, only to be executed by the groom on the wedding night for fleeing. Burning for revenge, he scoured the world for a cure for his rare medical condition from both righteous and villainous side.

Countless years go by, and finally Su Yun not only found a way to cure his rare condition but also gain immense knowledge on a myriad of martial techniques.

But before he could fully cure himself, he received news that the groom suffered an assault that damaged his internal organs. Rather than wait for decades to become fully cured, Su Yun decided to hatch a plan for the assassinate of the groom. Unfortunately, he underestimated the strength of the groom’s family and was killed instead.

Then he regains consciousness. He comes to a realization that he went 15 years in the past. This time, he vowed to protect Qing Er, but first he must cure his rare medical condition. Will he learn from the mistakes of his previous life or is everything still set in stone?

- Description from Novelupdates