Give me your power!!! Ye' ol bastards of spirits!!!!

[Orion]

If later I wanted to make moves and such that allow Nova to be possessed by souls and such, would I need an ability or not? If so what would I need?

Possession allows you to control other PCs. If you're being possessed by NPC souls for writing flavour, you wouldn't need anything. As soon as you want to affect others with them, though, you'd need Possession.