Gucheongugeom

Yeon Jeokha had to suffer years of abuse from his father's first wife for being the favored second wife's son. His fortunes change upon finding a mirror with a spirit who teaches him the Nine Heavens Sword Art, a powerful technique his father created. After an arduous decade of training, he successfully escapes and heads to the mountains, where he joins the Obong Outlaws as their strongest member. But he soon learns that the stronger he gets, the more enemies and rivals are bound to follow...

(Source: Tapas)