This might be heavy spoilers -
MC started out as a beta but was changed into something between a beta and omega by the ML. ML is a special kind of alpha known as a ghost/phantom(?) that can change a beta into omega by repeatedly knotting them. MC is also a special kind of being known as a "diamond dust" whose pheromones can only be sensed by a golden alpha but acts like a beta otherwise. By the end of the series I think the MC was about 50% changed to an omega. I'm not sure if he turned fully into an omega in the side stories but I assume he did

Novel readers, I have a question for you: Is the uke an omega or not?