I Became a Dark Fantasy Villain - Chapter 86

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

The head of the London Association of Mages, the most powerful Saint Archmage in the world, Audrey Davis, accidentally transmigrated to another world due to a magic accident. She was an 18-year-old human girl.