I have a question to ask... Why is Se Gi only one who has that kind of red tattoo on his back but other personas…
It's possible that male Do Hyeon created a personality with his real name Shin Se Gi beacuse his real one had been stolen and he wanted to keep it somehow. And maybe that's why Se Gi is that strong. And I agree that he fell in love because of memories and some kind of attachment. I think that the main reason why Se Gi can't be the owner is that he would know about it and as a result wouldn't say that Do Hyeon created him (espepecially if we take into consideration his personality :P). Or maybe I am wrong and he didn't say that. Hmm