Dimensional Descent - Chapter 6: Changes

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

To exist in a certain place, at a certain time—it's always either by chance, or by choice.But sometimes,There is a third force.One that doesn't ask.One that doesn't explain.It simply places you—wherever it wants.Arséne had always been dragged into places he never chose.Situations he never asked for.Realities he never belonged to.And when, at last, he decided to act on his own terms—To take the initiative,To move first,To choose…He simply died.

The main character is reborn as a character from a game he played in his previous life. This character falls into ruin along with the villainess, spending the last of their years together. A man named Kururi Helan.