That was a theory that me and a buddy of mine had but then that would mean that they both would have had to have concieved on the same day and gave birth on the same day because the "twins" share a birthday, the odds of that happening are astronomical. It would also mean that they are just half siblings which if that is the case then that would ruin the whole story for me personally because they are supposed to be twins, the fact that their sexual relationship is so....taboo is because they are supposed to be twins. If they are only half siblings then that's nearly as bad as stepcest. Im not saying that it has to be twincest for me to enjoy it but for THIS story the twincest works, its what makes their relationship special, they have that twin bond that evolved into a more romantic/sexual relationship. If it turns out that they are just half siblings then that all goes away, hence why it would ruin it for me personally. So im still hoping for my theory of rose being the mother to both of them.
Could be, but it could also be that they (
Adam, Anna, and Rose) simply lied to the "twins" about their birthday so that they could live a normal life.
And, I agree, a true 'twincest' is miles more interesting that halfcest, but keep in mind that half-siblings don't usually grow up together in the same household - let alone believing they are twins as well. To MC and Kat, their bond is that of twins, even if my theory proves correct and they aren't actually twins.
So far, though, MC and Kat are probably the first sibling incest story that doesn't somehow feel weird at all, since they have been shown and described by various characters around them as
unnaturally close from childhood.