Forgotten title: Korean novel (I think). Still being translated. MC is weakest rank hero with no powers, only physical ability and weapons. He's a 10+ year veteran hunter, which is supposedly rare because people at his rank usually die/retire. Suffering from an illness and after getting kicked out of his guild, something makes a contract with him. He starts to hunt MCs in exchange for life and one of their abilities. One of his new powers is swordsmanship and magic. Thank you! I caught up a couple months ago but forgot to write the name down!