Snape and Harry are werewolves. However you want to make this happen. Maybe they were both bitten by Remus in Harry's third year or maybe Snape was bitten in his fifth year and Harry another time, or maybe Harry was born like that in a sort of Darkest Powers AU (which I'd be thrilled if you decided to do).
- Remus helping Severus care for Harry. If you're doing a Darkest Power AU, he doesn't have to be a werewolf, but he has to be able to interact with Harry and Snape in their werewolf form.
- Perspective from a changed werewolf.
- How they became a werewolf. It doesn't have to be in vivid detail. A brief sentence could work.
- If a longer piece, it must have more than one perspective. I.E. it can't all be told through one character's eyes.
- Severus and Remus have another cub they're caring for like Ron, Hermoine, OC, Ginny, Luna, etc. (It can be more than one)
- If one if the other cubs is close to Harry's age (it can be a few years difference)
- If you explore the werewolf mythos more than the book
- Remus and Severus are a couple (especially if they become so through the course of the story)