Asura

Once there was an emperor's vassal who journeyed abroad to discover the secret of immortality. A lifetime went by, and the emperor and empire fell to dust. The vassal, now known as Chief, returns to the realm, bringing with him a boy of mysterious origin and immense power named Asura. In this unfamiliar world, Chief and Asura must reckon with peril and unrest among martial arts sects ruled by the nefarious Fort Sovereign. One thing, however, is for certain: the realm will never be the same.

(Source: Webtoon Entertainment)