Ci Nian is intersex. Intersex people have sex organs that don't simply fit into male and female boxes. They are usually a mix of the two. They are also not that rare (according to Planned Parenthood, about 1-2 of every 100 American may be intersex), but most people are never diagnosed so it goes unnoticed. So in Ci Nian's case, he outwardly presents as male, but also has ovaries and a uterus and can therefore have children. Irl, fertility for intersex people usually is pretty low and Ci Nian's situation is very unique, but it's still a possibility. I'm not a doctor tho so if you want to know more, I'm sure there's other resources to read about this if you are interested.
hello i don't understand why men can get pregnant in this manhwa hahaha this is not omegaverse right? so how tf he can get pregnant i really confuse right now