I Am in Seclusion to Cultivate Immortality, but You Tell Me This Is Martial Arts.

The protagonist Cui Heng traveled through time. At first, he thought it was a world of immortality. He met various protagonists, some from humble origins, some who brought peace to the world, and even some who were peerless geniuses, but met with sudden misfortune. He vowed to stay in seclusion until he could protect himself. After three hundred years of seclusion, he came out and discovered that this was a world of martial arts. This novel and its characters are purely fictitious. Any similarity is purely coincidental and should not be imitated.