i am basically 99% certain that shes his little sister with amnesia.
That does feel like it's maybe the best explanation, but at the same time it doesn't really feel like that's how the story will go. It's a bit too . . . easy? This story hasn't exactly taken the easy way out of anything so far, it doesn't seem likely it'd start now.
Maybe the better thing to be asking is how this essentially random person they've just found would be able to induce the kind of intense feelings that are needed to create a devil? And particularly how they might do so in a way that would link them tightly to Woo-Min Lee? Because it seems rather unlikely that he'll end up being just "the person who just happened to be there", it's got to be something more significant than that . . .
