I have a thought maybe she is half demon, hear me out. early on in the story where they are playing that one board game the truth or dare one, there is a part where she has to tie the male main character down with a rope, after doing the mission of the card, she continues to step on him enjoying the feeling. That is not something an Angel would normally be into, also later on the island she find the toy gun that she remembers playing with back when she was a kid and says that she remembers drawing a little drawing on it but she can't remember what it is. she they finds a drawing that I believe is the same one on the toy it's self. If that island is in the demon world, how would her old toy get there? and now she is acting more blunt and showing her feelings to the male mc. looks like to me, she has two people in her body, her main one is the angel and the second one is the demon. Now don't get me wrong I like the idea that the ring is doing those thing to change her behavior, but there is no way! as of right now (Chapter 121) the ring as only been able to make there body's lock in place or say how they feel but not fully take over, but the ring is still a good pick for what changed her, in the last part before we cut to the male mc waking her up it shows us the ring on her hand, but this can just be telling us that she past out thinking about here wish. there is also the fact some people thinking it's the headband she got from the male mc's sister but we can see that she didn't put it on before going to bed also we can see it's not on her head with the pic we get of her head. "maybe she's hiding it" you think but again we can see it clear as day on his sister in the two forms she has. Again I like all the theory's about what happen I'm not saying they are wrong but this is my own thoughts on this. hope you like my theory.