The Iced Autumn

Related by some chance Hannah and Hiccup which have now become the autumn siblings soon learn they are meant to be guardians. Hannah soon becomes friends with Lisette who is daughter of the moon and also now as Mother Nature. Hannah's worst friend and also assigned parter Jack Frost is a big nuisance in her role as spirit of autumn and it doesn't help that he's a family member of Lisette her best friend. But she soon learns to laugh at his games and jokes and finds a liking of the spirit of winters presents. Then a strange unknown dark fog is slowly starting to cover the globe making children loose memory of the story's their parents told them of the guardians. And now they are not sure how to stop the course of this fog before it wipes out every memory the children have about the guardians...forever.

(Yes this is a crossover of How to train your dragon)