Mirrors for the sky (HTTYD2 + HICCSTRID)

While Hiccup is doing his night flight with Toothless, he observes a little light on a side of the mountain. He lands not too far away from it and prepares himself for a fight in case it was an enemy, but when he manages to see what was there, he remains schocked. Curled near a pure white dragon of a race he has never seen before is sleeping a beautiful girl. She has pure white hair, pale skin and she wears a simple white dress, long to her feet.
But what will happen when Hiccup finds out she's his twin sister...?
She is like an angel, fallen there, in the middle of the forest. Her name was Rayn...and she owned a terrible secret...