I don't really think anything of the female form of the MC...he's a shapeshifter, can have any form. I don't think that it's indicative of having a twin. If the MC has anything remotely close to something like a twin then it was either absorbed before birth to be revealed later(though I doubt it), or it's Charlie. Though Charlie is 2 years younger than the MC so probably not birth twin...not unless there is some kind of time distortion shenanigans at play. But I think Charlie will be very important to the MC's growth at some point. Not sure if he'll end up having to fight her and absorbs her or if they'll be forced to work together by some circumstances or what but I think something big will happen between Charlie and the MC.Because of how op power twin type is, it's the only way I see mc going to gain an edge over currently high-ranking monstrous power of all those at the top and once again I also speculate this because of his female side, he was also kind of feminine looking before his transformation. Who know may be he get to meet one of the kings of the monster world and they grant him a boon of sort in the next update.