Okay so this random doodle was supposed to be another of my Harry Potter Jelsa AU with Elsa wearing glasses, but then it turned into smexy fox Elsa with the long bushy tail and a lightbulb goes ding in my head.
For my Celtic AU idea:
Anna and Elsa are fox fae, with Anna being a red fox and Elsa being a white fox. Anna has powers over Spring while Elsa retains her powers over Winter.
Jack is a gifted young sorcerer who is apprentice to North. He meets the sisters while participating on a hunt with the townsmen, but after sensing their true nature, he tricks the townsmen by casting an invisibility charm on them. Anna is sent to return home, and once Jack is alone, Elsa reveals her human form to him, who he almost instantly falls for.