Another plot could be that Snape and Harry are in the house as part of a secret mission. They have to find a hidden magical artifact within the house. As they search, they face various magical traps and challenges. In the process, they learn to rely on each other's skills. Harry's courage and Snape's knowledge combine to help them overcome the obstacles.
Maybe they are trapped in the house due to some magical curse. While they are alone, they are forced to confront their past issues. Harry might question Snape about his relationship with his mother, and Snape could finally open up about his true feelings and the sacrifices he made. This would be a very emotional and character - developing plotline.
At first, their relationship would be tense. But as they spend time alone, they might start to understand each other better. Harry could see that Snape isn't just the mean teacher he thought he was. Snape might also realize that Harry has more depth and strength than he gave him credit for.
One possible plotline could be that Snape initially hides his relationship to Harry out of fear or a sense of duty. He might secretly protect Harry more than anyone realizes. For example, his constant bickering with Harry could be a way to hide his true feelings. Another aspect could be how Harry discovers the truth. Maybe he finds some old letters or a hidden memory in Snape's Pensieve. This revelation would completely change Harry's perception of Snape and his own identity. It could also lead to a complex relationship between Harry and his mother's memory, as he would have to reconcile Snape's role in her life with his newfound knowledge of Snape as his father.
One possible plotline could be that Harry discovers a plot against Snape before it's too late. Maybe he overhears some Death Eaters planning to ambush Snape while he's on a solitary mission. Harry then uses his invisibility cloak and magic skills he's learned over the years to outwit the Death Eaters and save Snape. This would show Harry's growth as a wizard and his ability to set aside past differences with Snape.
A plot could involve Snape's deaging being the result of a dark magic experiment gone wrong. Harry and Ginny initially suspect foul play but soon realize that Snape is truly a child in mind and body. They decide to protect him from those who might want to use his situation for their own gains. As they do so, Snape begins to form a bond with them, especially with Ginny, who he sees as a sister - like figure. Harry, meanwhile, has to deal with his own mixed feelings towards this new Snape, as he is constantly reminded of the old, often - hated Snape, yet also sees the potential for a new beginning.
One possible plotline could be that Harry travels back in time. In this scenario, he stumbles upon a young Severus Snape being bullied by some older kids. Harry, with his knowledge of Snape's future importance and his own sense of justice, steps in to save Snape. This could then lead to a change in their relationship dynamic. Instead of the animosity that exists in the original story, Snape might view Harry in a different light from the start, which could potentially change the whole course of events at Hogwarts in the future.
One possible plotline could be that Harry breaks a major Hogwarts rule, like sneaking into the Forbidden Forest. Snape catches him and decides that a severe punishment is in order, which in this case is spanking. Another could be that Harry fails a very important Potions test repeatedly, and Snape, frustrated with his lack of progress, resorts to this extreme form of discipline. However, these are all just fan - created ideas and not part of the official story.
Well, a plotline might involve Snape initially being in denial about the pregnancy. As it progresses, he could start to form an unexpected bond with the unborn child. There could also be a plot where other characters find out and either support him or try to use it against him. Maybe Voldemort discovers it and tries to manipulate Snape in a new way because of this situation.
One possibility is that they have a heart - to - heart conversation. Snape could finally open up about his past actions and his complex relationship with Harry's parents. Maybe he tells Harry about the sacrifices he made to protect him all those years. Harry, in turn, might come to understand Snape better and see him not just as a strict and often - hated teacher, but as a deeply flawed yet ultimately heroic figure.
There could be a plot where Snape's muteness is a secret that he tries to hide from everyone at Hogwarts. The story could be about how he manages to teach Potions and be a double agent for Dumbledore all while keeping this secret. Or perhaps a plot where his muteness is a magical experiment gone wrong, and the story is about his journey to reverse it. Along the way, he might discover new aspects of magic and his own identity that he never knew before.
One possible plotline could be exploring the hidden family connections between them. Maybe Harry discovers that he has some distant family relation to Tom Riddle through a convoluted family tree. This could lead to a conflict within Harry as he tries to come to terms with having a relation to the dark wizard. And Severus Snape's family could be intertwined in this discovery, perhaps his family having some role in the past that led to the current situation.