He almost broke last chapter and now she's giving him false hopes? I fully expect him to snap at her next scheme and it wont be easy for her to repair him.
@crittlercrittler is right
The whole point of "100 days" format is that it is a constraint that encourages to keep the story moving. It's about the characters living in the now and how we live along with them in those 100 days. The flashbacks and the characters guiding use through those...
Maybe Mary was trying to summon a powerful being. Neah examined Ren and learned that he wasnt which is why Neah is trying to take him away even after Mary already accepted him.