One interesting plot could be Snape taking in Harry after the death of Sirius. Snape, despite his initial reluctance, realizes he has a responsibility. He starts to train Harry in advanced potions and dark arts defenses in secret. This could lead to a unique bond between them as they gradually understand each other better.
One interesting plot could be that Hermione discovers Snape is ill or injured in a post - war scenario. She uses her vast knowledge of magic to nurse him back to health. During this process, they start to understand each other better. Snape, who has always been a rather aloof and misunderstood character, begins to open up to Hermione, sharing his past traumas and the reasons behind his actions in the war.
One interesting plot could be that Snape, in raising Harry, discovers a new side of the boy. He realizes that Harry has a natural talent for potions that was overlooked. Snape starts to teach Harry advanced potions techniques, and they form a sort of begrudging respect for each other. Harry begins to understand Snape's past and why he was so bitter, which changes their relationship for the better.
Perhaps in this fanfiction, Harry discovers some secrets about his parents from Snape that Dumbledore had been keeping from him. This could lead to a whole new understanding of the wizarding world's politics and relationships. Snape could be forced to protect Harry not just because of his loyalty to Dumbledore, but also because of his newfound connection with Harry.
Well, in some fanfictions, Snape trains Harry to master the art of non - verbal spells more effectively. This gives Harry an edge in duels. Also, there could be a plot where Snape trains Harry in the history of dark magic not to use it, but to better defend against those who do. It's a way of making Harry more well - rounded in his magical knowledge.
One interesting plot could be that Snape, while teaching Harry, discovers a hidden talent in him for a very rare branch of magic. He then decides to secretly mentor Harry in that area, leading to a unique bond between them.
One interesting plot could be a magical duel between Harry and Snape where they both use unexpected spells. Harry might draw on some newfound knowledge from an ancient magic book, while Snape uses his years of experience and dark arts knowledge in a creative way.
In some fanfictions, Snape might dress Harry in an attempt to disguise him. For example, if there's a threat from dark wizards targeting Harry, Snape uses his knowledge of potions and magic to create special clothing or a disguise for Harry. This could lead to a series of adventures where Harry has to pretend to be someone else while wearing Snape - styled clothing, and they have to work together closely to maintain the ruse.
There might be a fanfiction where Harry takes care of Snape after a battle. He could be the one to tend to Snape's wounds, both physical and emotional. Since Snape has always been a rather closed - off character, Harry's attempts to get through to him and provide care could be a great source of character development for both of them. Harry might use his Gryffindor courage to break down Snape's walls.
Maybe Snape catches them in the middle of a magical experiment gone wrong. Harry and Ginny were trying to recreate an old spell they found in a dusty book, and the resulting chaos draws Snape's attention. He then has to decide whether to punish them or help them fix the mess.
One possible interesting plot could be Snape having to follow Harry Potter's lead in a dangerous mission. Maybe they are in a situation where Snape has no choice but to trust Harry completely, which is a big change from their usual relationship in the original books.