Honestly I think he's the one who brought her back and give her the memories. Most likely something happened in the future with corset that made realize his mistakes. And that could be why he remembers that something is missing that something is not right with cossette and that's why he doesn't remember the nightmare......ofc this is just a theory
(づ ̄ ³ ̄)づ
I think the one who brought her back was the blonde dude with blue eyes because he is a magician and he works in the tower of magic or something, and if you look at it, at zekes 13th birthday he mentions something and he retracts it back ( or he stutters) so Im assuming that he may know some things and its probably him that brought keira back to the past

Someone spoil me, is the father good or bad?? He keeps looking like he cares but he doesnt actually care or what??? Also, who is the damn ML? The knight? The magician dude?