Pregnant??

i'm betting that it probably has to do with a moon rabbit loophole, something like "he can only get pregnant whenever he wants to or is willing"

Or Haru has been taking some kind of supplement he was taught by his mother, who knew he was a moon rabbit, and isnt aware or hasnt shared that it prohibits conception.

Ooh that's a good theory

My theory is probably neither's fault but I do think that it may be from Neungso's inferiority complex. I think since he thinks of himself so lowly and still thinks of himself of the "burden" half-blood that he unconsciously doesn't want to bring bunnies like him into this world. The body works in mysterious ways and maybe his body may be rejecting the thought of children cause of his fear.