What could be the plot in a fanfiction where Snape is Harry's uncle?

Sure. In fanfiction, the idea of Snape being Harry's uncle can open up a whole new world of stories. Writers might imagine that there was a hidden family connection all along. This could change how we view Snape's actions in the original story. Maybe he was secretly looking out for Harry in more ways than we thought, because of this family tie.

Well, one possible plot could be that Snape uses some kind of powerful magic to transform himself into a female form and becomes Harry's mother. He could have done this to protect Harry in a more direct way, perhaps knowing some dark prophecy about Harry. And then the story could follow Harry's growth with Snape as his mother, dealing with the secrecy of it all.

One possible plot could be that Snape discovers his relation to Harry early on. He then has to struggle with his feelings towards Harry. On one hand, he might feel a sense of family loyalty, but on the other, he still has his grudges and past issues. Harry, on his part, might initially be in disbelief but then start to see Snape in a new light. This could lead to them working together more closely to fight against Voldemort, with Snape being more open about his knowledge and skills to protect Harry.

One possible plot could be that Snape stumbles upon Harry being bullied by Draco and his cronies. Snape, despite his initial dislike for Harry, is appalled by the abuse. He then secretly starts to protect Harry from further harm, which gradually changes his view of Harry and leads to a more complex relationship between them.

One plot twist could be that Snape is actually mentoring Harry on behalf of Dumbledore from beyond the grave. Maybe Dumbledore had some secret plan that he didn't get to fully execute, and Snape is now following through with it. Another could be that Snape discovers a new magical ability in Harry that no one else knew about.

Perhaps Snape finds Harry drunk in a secluded part of the Hogwarts grounds. Snape, being strict, would likely want to punish Harry according to the school rules. However, he might also be secretly concerned about what led Harry to this state. He could start an investigation into whether someone influenced Harry to drink or if Harry was dealing with some personal problems that drove him to this. This could lead to a series of events where Snape and Harry have more interactions than usual, and Snape might even end up protecting Harry from any potential backlash within the school.

Well, it could be that Tom, as Harry's uncle, secretly has magical powers of his own. Maybe he's been in hiding all these years. He could emerge to protect Harry from some new dark force at Hogwarts. For example, a new group of dark wizards that the regular teachers can't handle.

Well, it could be a rather strange plot. Maybe it's a situation where Harry is injured and Snape has to hold him in this way for some kind of magical healing process. Harry might be in a weakened state and Snape, despite their past differences, has to take care of him. This could lead to an unexpected moment of understanding between them.

The plot might start with a magical experiment gone wrong. Harry ends up with a special mark or power that makes him Snape's master. As the story progresses, Harry uses this power to make Snape teach him advanced potions and dark arts defenses. Snape resents it but has no choice. Meanwhile, Voldemort senses this strange new power dynamic and tries to use it to his advantage. This forces Harry and Snape to work together in ways they never thought possible to outwit Voldemort while also dealing with their own difficult relationship.

Maybe in the fanfiction, Voldemort devises a plan where Snape forgets Harry to disrupt the Order of the Phoenix's plans. Without Snape's knowledge of Harry and his role in the prophecy, things start to go awry. Harry has to find a way to make Snape remember, perhaps by going on a quest to find a magical relic that can restore memories. Hermione and Ron would be by his side, of course, providing their usual support and knowledge.