Cinnamon Bun - Chapter Four Hundred and Ninety-Two - Taking Your Leader with Me

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

Our protagonist was a Mexican who died on a flight, when he woke up he found Apollo who reincarnated him as the grandson of Gaius Octavian Turino (Augustus) the first Roman emperor, having a mission in hand to conquer the New World to save the Roman polytheist world and his existence.

On modern-day Earth, An Lin seems to have been abandoned by God.
When his father suddenly disappears, An Lin is left with his father’s immense debt, putting his life at risk.
After being forced to a rooftop by his pursuing creditors, An Lin is unexpectedly swept off his feet and brought to the ground safely.

Xuan Yi was transported into the fictional world and became an elder of the Black Sword Sect! The moment he entered the world, he was at the Sea-Splitting Rank!