MWAHAHA

But don't Omegas want to be fucked in the ass during their heats bc they feel empty and wants to be filled

You have a point, but bruh! the omega is in control, imagine this, the alpha being driven crazy by his pheromones begging him to let him fill him, knot him, fill him with his pups..but the omega is just there smirking down at him as he overwhelms his alpha with his scent, denying him. Then at the moment hes reduced to a whimpering sobbing mess, hed grant him relief by fudging him first then if hes generous, hed let himself be done. BUT that is..if the omega can like maintain his consciousness while in heat. In some mangas they immediately become super needy. I have a doubt that the omega in this one will, he seems really cunning. (Sorry if description is graphic )