I think Leon's just an omega. The residents of the Dark Fall can't reproduce by themselves so they need Leon to give birth.
That is possible but given it was not an ABO setting (not confirmed) we can just deduce that he got a special race that allows them to conceive.
I remember said that his race allow them to change when they take a mate so after Leon falls in love with Cliff, he can conceive and emit pheromones. I think, only Cliff who Leon regards as his mate can impregnate him.
Yeah, that's right. But it's a one-sided marking ig since Cliff left Leon (or he might be ded somewhere) so unless Leon breaks his longing for Cliff, he might take them four as his. wwwwwwww
My theory did not match since Mephisto pulled out ╥﹏╥
anyways, since it was clear statement that they can sense something alluring about Leon, I wonder if what his race really is. Coz I can't help but think that he might be in elven race that makes it possible to impregnate anyone since they have neutral gender or could they be have both functions as their race is limited and hard to conceive due to their idea of finding someone they'll love forever (lmao I'm getting carried again with my brain mush)