The Substitute Bride - Chapter 9

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

Gu Shanhai saw the great world of the heavens, and took the life of the third life.

The gods of the world forged an eternal Utopia with blood and fire.

The Red Dragon King led his knights to inspect the dynasty on which the sun never sets.

Scholars talked and laughed and swung their swords to draw thousands of miles of rivers and mountains, and strange demons opened their eyes and clawed to give birth to ghosts and monsters.

…

“Everyone is a player, you can’t call me abnormal because I don’t have digitization?”

- Description from novelbuddy

A man reincarnates in the body of a boy who suffered a tragedy, only to realize that he is in the world of My Hero Academia. What's even stranger is that his quirk seems to have the abilities of Nen and Haki.