The Speedrun Manual of Miss Witch - Chapter 10 - Deceit and the Church of the Savior Goddess

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

Xu Jun finally defeated the BOSS–the Dark Demon King, in this stand-alone, virtual reality game. When he wanted to go out to browse Weibo and express his mood, he suddenly encountered a game BUG and immediately passes over to the game world.

He became the man who finally took down the Great Demon King in this world. Gratifying! The attention of millions of people!

……However, he did not know the development of this world was not the same as the game, the Demon King did not die, rather his soul entered into Xu Jun’s body; this Demon King knows of all the stupid things Xu Jun does everyday…….

- Description from Novelupdates

Endless sky and infinite space, the cosmos isn’t some paradise waiting to be found, it is full of darkness and danger, death and terror of the great unknown. However, for that glittering swath of blue, we have no fear! For the longevity of men, we have no regrets! Nothing shall stand in our way because it is finally our time, our age! The age of cosmos exploration!

The gods visit my shop. I travel across countless worlds with them. But then… “This is my sword, the Heavenly Tyrant Blade.” “This is the Ruyi Jingu Bang.” “This is the lightning spear I once wielded.” Their payments are… peculiar.