One plot could be that Snape, under some dark magic influence, forces Harry to accompany him on a dangerous mission to retrieve a lost magical artifact. Snape believes Harry has some hidden power that can help. Another could be Snape forcing Harry to study a very advanced and dangerous form of magic, thinking it will protect Harry in the long run. And there could also be a plot where Snape forces Harry to enter a magically sealed area to face some long - forgotten threat that only Harry can potentially defeat.
There are several interesting plots. For example, Snape could force Harry to train with him in the art of Occlumency more rigorously than in the original story. He might be doing this because he has foreseen a powerful enemy who can read minds and wants Harry to be able to defend himself. Another plot could be that Snape forces Harry to join him in exploring an old, abandoned wizarding school. Snape suspects there are powerful spells and knowledge there that could be used against Voldemort. Also, Snape might force Harry to work with him to break a powerful curse that is slowly affecting the entire Hogwarts, believing Harry has a unique connection to the magic of the school that can help.
Well, a possible plot is that Snape forces Harry to help him uncover secrets about Harry's parents. Snape might believe that there are things Harry doesn't know that could change the wizarding world. Or perhaps Snape forces Harry to participate in a series of magical trials that are designed to test Harry's loyalty to Hogwarts. This could be because Snape suspects Harry of being influenced by dark forces. Another idea is that Snape forces Harry to enter the Forbidden Forest at night to find a particular magical creature that Snape needs for some potion or spell.
A common and really interesting plot is the idea of a time - turner being involved. For example, in some fanfics, James Potter goes back in time to understand Snape better. This allows for a whole new exploration of their relationship as James sees Snape in a different light, away from the schoolyard rivalries. It's a great way to rewrite their history in a more positive way and shows how they could have been friends under different circumstances.
Some unique plots include a fanfic where Snape and Harry are magically bonded and can feel each other's emotions. There's also a story where Snape is turned into a cat and only Harry can understand him, leading to some really interesting interactions. A different one is a fanfiction where Harry discovers that Snape was actually protecting him all along in a much more elaborate and secret way than in the original books, and they have to team up to expose a greater conspiracy within the wizarding world.
One of the most interesting plots could be Snape having to protect Harry in a very unexpected way. For example, in a fanfic where dark magic has been unleashed in a different form and it targets Harry specifically. Snape, despite his initial reluctance, realizes that Harry is the key to stopping it and has to put aside their differences. Another plot could involve Snape and Harry being transported to an alternate magical realm where they have to rely on each other to survive. They slowly start to understand each other's past traumas and develop a grudging respect. A third plot might be that Snape discovers a long - lost prophecy about Harry that changes his perception of him completely and he becomes his secret mentor in a much more involved way than in the original books.
There could be a fanfic where Snape survives the Battle of Hogwarts. After the battle, he and Harry have to come to terms with their past relationship. Harry realizes how much Snape sacrificed for him and the wizarding world. They start to build a new relationship, with Snape helping Harry to understand some of the more complex and dangerous aspects of magic that were once only known to Snape and Voldemort.
One interesting plot could be Snape raising Harry while secretly training him in advanced potions and dark arts defenses. Harry would grow up with a different perspective on Snape, seeing him as a strict but caring father figure. Another plot might involve Snape having to protect Harry from other dark wizards who suspect Harry's true potential. This could lead to some intense magical battles and Snape using his knowledge and skills to keep Harry safe.
A really unique plot could be Snape adopting Harry during a time when Voldemort is still a threat. Snape has to balance protecting Harry from Voldemort's followers and also from the prejudice within the wizarding community. He might train Harry in Occlumency more intensively, and in the process, they develop a deeper understanding of each other. Harry starts to see Snape not as the mean professor but as a complex person with his own traumas and reasons for his actions.
A common plot is the 'what - if' scenario. For example, what if Snape had confessed his love to Lily before she chose James? This often leads to alternate timelines where Snape and Lily end up together, and the whole story of Harry Potter changes. Another plot is the secret relationship plot, where Snape has a hidden relationship with someone (could be an OC or another character) that is related to his unrequited love for Lily.
Well, Harry could react with a great deal of suspicion. Since he and Snape have had a rocky relationship, he might think Snape is up to no good. He could try to gather his friends, like Ron and Hermione, to help him figure out what Snape's real motives are. Harry might also try to use his own wits and magic skills to outsmart Snape if he feels that Snape is being unfair or dangerous in his forcing of actions. He could also be very conflicted, on one hand wanting to trust Snape as Dumbledore did, but on the other hand being very wary due to their past interactions.
There are also fanfictions where Snape time travels and gets involved in the founding of Hogwarts era. This is a very creative plot as it combines Snape's character with the ancient history of the wizarding world. He might use his modern - day knowledge to influence the founding principles of Hogwarts or have interactions with the founders themselves, which completely changes the course of wizarding history.
In some fanfictions, the flagrum fire whip is enchanted in a way that it can control emotions. Snape has to figure out how to break this enchantment. This plot is full of mystery and suspense as he tries different spells and potions. It also shows his intelligence and determination. Also, there are fanfics where the whip is a key to a hidden magical realm, and Snape is the chosen one to explore it. This takes Snape on an adventure full of magical creatures and ancient spells.