...I would have thought that those two would be restlessly searching for Erin's fragments if they wanted her back, not going to dad and crying an ocean to make him fix their mistakes... Besides, if there are still fragments left, why don't they go and search for those instead of using Rin as bait? For now she's as safe as she can be and if they go hunting the fragments sooner or later they will bump into the guy collecting them too.........
And why turning back Rin's body to a baby's? Maybe the punishment is still working and somehow Erin dies everytime her body matures to a certain point?