MTL - As the Minor Gay Rival in Het Novels - Chapter 36

This book was inspired by My Hero Academia: Adaptation“Who decided being quirkless means you can't be a hero? Those are just rules made by people who never tried to break them.” When a battle-hardened warrior dies in one world and awakens in the body of a quirkless boy in another, the rules of heroism are about to change.Armed with combat experience from a darker realm and an iron will forged in warfare, he sets his sights on U.A. High School - the pinnacle of hero education. But in a society where superpowers are everything, his approach to strength might just shatter the entire system.Behind a gentle smile lies the mind of a warrior. As he builds his power through unconventional means, one thing becomes clear: rules were meant to be broken, and this world's definition of “hero” is about to be rewritten.Sometimes the strongest ability isn't a quirk at all. It's the will to change everything.

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

Seven years ago, at a charity gala, she unintentionally became his cure and ended up pregnant with fraternal twins.