One interesting story could be where Snape uses a collar on Harry as a form of magical protection. In this fanfiction, the collar might have special enchantments that keep Harry safe from dark magic. It could also be a symbol of Snape's hidden care for Harry, despite their often tense relationship in the original series.
There might be a fanfiction where the collar is a key part of a magical experiment. Snape puts the collar on Harry to study his unique magical abilities more closely. This could lead to some tense moments as Harry initially resists, but then realizes the importance of the experiment for the greater good. For example, it could help in finding a way to defeat a new dark wizard threat.
In some fanfiction, the collar could be part of a magical contract. Snape, for some reason, binds Harry with the collar under a contract. This might be related to Harry's inheritance or a mission he has to undertake. As the story progresses, Harry and Snape have to work together to fulfill the terms of the contract, which also helps in building an unexpected bond between them.
One idea could be that in the fanfiction, the collar is a magical device used for protection rather than a form of control. Snape might put it on Harry to shield him from dark magic threats at Hogwarts.
The plot could involve Snape collaring Harry as a form of punishment for some misbehavior that endangers the wizarding world. But then, as they are forced to interact more because of the collar, they start to understand each other better. For example, Harry might learn about Snape's past and his true loyalties.
It can show a more complex side of their relationship. For example, if the collar is a means of control, it forces them to interact in new ways. Harry may initially see it as a sign of Snape's tyranny, but later discover there are deeper motives, like Snape trying to protect Harry from a hidden danger. This reveals a different layer of Snape's character and his true feelings towards Harry.
One interesting Snape and Harry fanfiction could be one where Snape mentors Harry in a more private and less hostile way. They could bond over potions and Snape could finally see Harry as more than just James Potter's son.
One interesting Harry Snape fanfiction could be one where Snape adopts Harry after the death of his parents. In this story, Snape has to overcome his initial dislike for James Potter's son and gradually forms a unique bond with Harry. It shows a different side of Snape, his capacity for love and care that was hidden beneath his cold exterior in the original series.
One interesting Snape - Harry fanfiction could be where Snape finally reveals his true feelings about protecting Harry to him. Maybe in a moment of danger, Snape confesses that he was always secretly looking out for Harry because of his love for Lily.
One interesting deaged Snape and Harry fanfiction could be about Snape being deaged to Harry's age and them having to work together on a special project at Hogwarts. They might start to see each other in a new light, away from their usual teacher - student dynamic.
One interesting fanfiction could be where Snape uses his cane not as a tool of punishment but as a magical conduit in a situation where he and Harry have to work together against a new dark threat. In this story, the cane might hold secrets of an ancient magic that only Snape is aware of initially.
One interesting aspect could be the exploration of Snape's complex character in a dominant role over Harry. It might show a different side of their relationship, perhaps with Snape guiding Harry in a more forceful way in magic studies. For example, he could push Harry to master difficult spells faster.
A really cool fanfiction could be set in an alternate universe where Harry, Snape, and Draco are all part of a secret society in Hogwarts. They have to keep the society's existence and purpose a secret while dealing with their own personal issues and rivalries within the group.