Married Thrice to Salted Fish - Chapter 45

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

An orphaned boy with dreams of making it big through being a blacksmith is given a once in a lifetime chance to succeed when he's taken in by an odd pair - Eggor and Ella. While former teaches him the arts of craft, the latter teaches him the mysticism of cultivation, granting him two paths to tread in this life.

Master said, the woman I held in my hands, I must protect for the rest of my life.