It is not omegaverse, how are people getting that idea? It's a cult related thriller and Seong Su was habitually mentally/physically/sexually abused as part of it. While there are theories for what the role the cult leadership had him play was, there's never been a comment by the author even alleging towards omegaverse. It wouldn't even make sense at this point, since noone else in the story has mentioned that?? The mystery surrounding his role and his kids can be explained by the high-control and coercive nature of a cult's rituals.
I guess when I looked up this one online it got mixed up with another story by the same title, and other things made me suspicious, but I hope you're right.
This is an omegaverse, right? I didn't know....I think I'm gonna drop this..for now