Maskbound: The Ultimate Hunter

Ossian spent four years carrying equipment for hunters who called him useless. When his guild cuts his rope inside a Gate, they expect the classless porter to die with their mistakes. He survives by killing a monster with a broken ceremonial mask. The victory awakens a system built for something that was never human. It registers Ossian’s ordinary face as his first mask. Monsters he kills can now become new faces, giving him their bodies plus abilities. Mastering a mask leaves part of its strength with him forever. He can also give a mask to another person, but that choice lasts for life. Every transformation raises his Identity Fracture. Worse, the system keeps treating allies as servants meant to obey him. With Calista, a discarded spearwoman who refuses pity, Ossian begins building a guild from the people powerful hunters threw away. He needs monster power to destroy the guild that buried him. He just has to remain human long enough to use it. — Description from novelcodex.org