Shiva: The Lady of Winter
First encounter
PCs are desperate and trapped In a blizzard on top of a great glacier in the northlands. The face of the lady will appear in the storm and blowing snow. She will offer to grant a boon in the form of a spell to a player in exchange for their help. Spell can be called Inner Fire or Eternal Warmth or something along those lines. One PC who agrees to help her will learn the spell that will make the player and all allies close resistant or immune to cold for 1d4 rounds.
Problem
The great glacier is diminishing rapidly. She will do anything to make it grow strong to return it to its former glory. She cannot leave this mountain but the PC can… With her help anyway.
Needs
The essence of winter. Magical essence of pure cold in the shape of a crystal, orb, or some other form that can be found throughout the land. They are harvested from ice elemental creatures who occasionally escape the the outer elemental planes where the planes of water and air converge. Mages and collectors seek these out for their magical essence that can be used for multiple purposes. They are also highly valuable.
Rewards
After descending from the mountain, Shiva will appear one more time and teach the same PC how to call frost in a basic form by manipulating the moisture in the air and temperature. It will be enough to freeze water and a basic offensive cold spell like an ice dart or frostbite. If an essence of winter is gifted to her, the glacier grows and she becomes stronger and gifts you a piece of her power in the form of new, more powerful cold spells (cone of cold, blizzard, all the good stuff).
Communication
Drawing the face of the lady in frost or ice (can be made in water with the basic cold magic learned) her face will animate and the PC can speak with her. Essence of winter can be absorbed into the ice and sent to her.
Enemy
Her brother, Ifrit. A djinn of pure fire who lives in a volcanic mountain near her mountain is her enemy. He wants the world to burn in volcanic ash. He seeks to heat the atmosphere so that he can lord over a newly formed land of fire. Once he finds out about his sister’s growing power, he becomes angered and will summon creatures of fire to end the party.
Allies
Northmen know of frost-callers from legend and lore. When they witness the abilities gifted by the lady of winter, they will do what they can to help the PC.
Thought your idea was awesome and had to give it a go. I Always liked a good fire/ice dichotomy and I’m a final fantasy fan.