Fuyu is ancient, a god of frost and winter. He was a majestic and terrible fox-like beast, ruling over the frozen wastes for many centuries until his brother Natsu betrayed him, burned him alive, and cast his body down a cliff. From the ashes a new form sprung forth, much smaller and weaker, looking like an arctic fox kit.

A small and fragile mortal found Fuyu in the forest and adopted him as a pet. Fuyu does not consider himself a pet, but he accepts the mortal's praise, food, and affection.