Divine Throne of Primordial Blood - Book 7, Chapter 99: Battle Against The Gods 3

As a promise, he went out into the world as an assassin. 3 years later, after becoming the Supreme Assassin, he gave up on everything he had and returned to the ranks of ordinary people. But one day, Kismet, a mystical game created by the National Research and Development had appeared.

Enigmatic hands, spectral frame, and one cunning strike just like the swing of the Grim Reaper. The Supreme Assassin takes on the mystical world, and how his legendary tales sets off, progressively ascending the altar to becoming the best.

- Description from Novelupdates

[I was reincarnated as an F-class Hunter.

…it’s a problem because they don’t treat me that way.]

My whole life, all I wanted was power.

I churned the world into rivers of blood and eventually gained the title, “Demon Lord of Strength”. However, all this became useless when I lost to a party of heroes.

But what can a loser say? As I laid dying, I was forced to listen to the hero’s gibberish:

“If you are born again, I hope that you will live a kind life!”

But huh? When I opened my eyes again, I was back in the past.

“What do I have to do to live a kind life?”

This is the beginning of an ex-Demon Lord’s journey to live a kind

Upon opening his eyes, Muyang realized that he found himself in Dragon Ball’s world filled with dangerous people like Vegeta, Frieza, Cell, Majin Buu.