Adeline

An ice fairy who's supposedly older and more experienced than the main cast. The only thing I established about her and it doesn't even matter in the story.

Gets stuck on Earth along with, but unbeknownst to the main cast. Doesn't know they got stuck, either. Both parties learn of each other's presence near the end of the story. 

Adeline is a very half-assed deus ex machina who revealed herself by saving several protagonists. She wasn't even mentioned once prior to her grand entrance.