Replying...
Intro. On a night like any other, after the events of Frozen 1, everything was normal until a strange comet shot across the sky. Anna noticed it and went outside to check, the comet having a strange purple glow about it as it shot off into the horizon and vanished. Leaving a brilliant trail of purple light behind it. Wow!!.... that was so cool. Anna exclaimed as she gave a warm smile and went back inside, unbeknownst to her, her older step sister Elsa, had wished for a fallen star, a chance to redeem herself but was lost in the depressive memories of her own weakness. as Elsa sat inside of her new ice castle, a mysterious purple glow emanated from somewhere outside, she went to investigate it, she was not seen again as a new storm descended upon the country, no... this time it was the whole world in danger and Elsa is gone!! you are Anna, setting out to find Elsa who's lost, again but the ominous clouds loom ahaed as Anna is riding along in her carrage, when suddenly....

Anna and Elsa AU Frozen 2 to 3

@Sean