It’s a revenge story isn’t it and the Protagonist isn’t going to end up happy right :/
It's not revenge. The synopsis said they have feelings for each other though it was never shown in the past. And now you can see the image in Seo-In's eyes of how much he wants YeongWoon. And YeongWoon had that dream about Seo-In as well after having seen HaeYool w/ him (when they met up privately at the hotel room 702) and also in his thinking process that if he goes to work for Seo-In and rekindle that relationship that they would end up going beyond the friendship, crossing the line of no return... You can see HOW MUCH they THINK about each other in their thought bubbles and the intensity of their interactions...
they’re both asperian- nux being half asperian/half human, Owen being full asperian- owen explained on that world they have soulmates and like in most omega verses one in the pair can get pregnant regardless of their sex. In this story however there seems to be a twist where like others have pointed out, the one putting it in got pregnant, what is happening is probably that the asperian can adapt their bodies for their mates and he’s developed a way to carry their offspring- perhaps similar to seahorses like some have said.