High School DxD - Volume 25 Chapter 7-2

A great demon king who came from another world to conquer Earth. To save the Earth, Li Luyou could only first take care of this great demon king… a little girl proclaiming herself Her Imperial Princess.

- Description from Novelupdates

In the Solarian Empire, people were divided by their blood. The nobles enjoyed their life in wealth, with fine wine and amazing food. They reigned supreme over the commoners. The only reason they were able to do this was that they had knowledge of the most powerful force in the world - magic. The nobles controlled their knowledge from easily going to commoners, making it harder for them to learn magic.

Leo, a young orphan in Solaria, had an incredibly powerful affinity for magic. He didn't even know about it because he could never learn magic- he was too poor to try and learn from any magic academies. He was just trying to survive the streets of Solhaven until he found the lost tome of the Arcane Emperor.

"I can beat a 7th Circle Mage."

"Wow! You must have trained for many decades. How old are you?"

"17."

"..."

The world was going to be turned upside down.

There’s a legendary Bishoujo Game that has become popular among Japanese gentlemen.

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