MTL - Immortality: My Spell Upgrades Infinitely - v2 Chapter 318 4 Realm Daojun Aoki Old Man

Kai is the hardest working warrior in his generation... and the unluckiest. In a world where most people receive magical skills, classes, or cultivation, Kai has nothing but his wits and his strength. His only choice will be to forge a new path against fate, no matter where it takes him.

Savage monsters pour endlessly from the wasteland, threatening the survival of civilization itself. They say that human strength isn't enough and only those gifted with destined powers have a chance of making a difference. Kai is hungry to fight in that war, to be someone who matters. That hunger will take him across a world stranger and more terrible than he could possibly have imagined.

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

The youngest princess of the country of Stellaus, Marietta, was betrothed in a political marriage to the General of the great militant country, Oltaire. General Belvant was often said to be strong, a fierce and terrifying god of a warrior. On the other hand, Marietta was a delicate flower of a princess. Everyone felt pity for poor Marietta’s situation, however, the truth was that Marietta found the General very dreamy… The story of a 30-year old General with a scary face (who was actually quite nice), and the tiny and adorable 18-year old Princess in their times of conflict and of lovey-doveyness.

The most feared Assassin in the world died because of vengeance.