I Declare Vengeance! by Daeyuma

Summary

All Yun Jejin wanted was to succeed in life by climbing his way out of misery and misfortune – but his life takes a nosedive when he ends up a debt collector’s target, all because he co-signed a loan for a friend. With nothing to his name and revenge on his mind, Jejin decides to pay it off the hard way…by becoming a gangster himself. But unbeknownst to him, someone’s been watching his back: Choi Taekmu, a thug with a heart as big as his muscles, and a not-so-secret crush on the rookie mobster. As the two work together toward Jejin’s goal, vengeance might not be the only thing that’s coming in red hot…