The Debt Collector of the Three Borders

Abandoning his life in underground boxing, a hidden-skills mercenary. Lone wolf Chen Yan and his sworn brothers step into the lawless Three Borders, entering the game as the lowliest debt collectors. Drug networks, telecom fraud hells, organ black markets, and headhunters in the deep mountains prey on people everywhere. Plots and knives, framed poisonings, love and hate burning hearts—every step is bloody. He hides his edge, showing weakness, fooling the world with a simple face, suppressing darkness with iron blood, rising and falling in the border's bloody sea, defying fate to turn the tables and ascend to the unshakable underground overlord. — Description from novelcodex.org