My initial thought was Matthew's, but Myeong Ji will probably try to rip it out of her chest.  Then Joo Ran popped into my head, but I have no real reason to think that.  Maybe because she's so good with the children.

 I've finally settled on Chan Seong. In the last few episodes I think they're going to clean house so to speak and  get back down the original pahbos and crazed killer. I'm thinking w/n in the next 2-3 episodes Mo Ne will succeed in killing Chan Seong  in a way that won't damage his heart, which will coincidentally be a match.  Maybe it'll also be our opportunity to find out why he hates Min Do Hyuk so much. I really never bought that it was because of Mo Ne.

I just saw the actor's IG post and I think that your theory is true.. after seeing his post I thought that ep 14 is the season finale🥲

 professionalfangirl101:

i think it will be yang jin mo...feels like he will die protecting someone.  maybe he will get tested beforehand and then finds out he is a match and somehow will think that this is his chance to atone for what he did..something like that. Kinda on brand for the level of drama this show has