Heroine Netori - Chapter 9: 18+

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

Finding himself in an Last Airbender without an airbender around, a transmigrator waterbender goes on an adventure to stop the worst from happening to him.

Skyler's story was typical. He was publicly labeled a waste with no future as a Light — awakened individuals capable of wielding elemental powers. He thought that would be the end of it. But no, apparently that was not the case.He was teleported to the 'Battle Royal' to fight, even though he had zero powers and his age and potential were 100% ineligible!To make matters worse, he was not even the protagonist or transmigrator! He was just a freaking side character destined to die young in the story! And his death served only one purpose — to bring his sister closer to the protagonist!What a pitiful ending, right?However, unbeknownst to all, he wasn't meant to die but to become the best in two other realms, and they had altered the fate of that powerful King. Yet, there was a tiny problem — he didn't remember how he became overpowered in his past.

In the eyes of outsiders, Yan Ruxu’s conditions are extremely good: good looks, high education, a high salary, and a high position, but there is a fatal flaw: she is divorced, with a three-year-old child. Yan Ruxu didn’t care what others thought of her, she just wanted to raise her son well and live her own life.

- Description from Novelupdates