One possible plotline could be Harry and Severus being forced to work together on a dangerous magical task. They start off hating each other but gradually come to understand and respect one another through the trials they face.
Hermione is often a popular character. She can play the role of the mediator or the one who tries to figure out what's really going on between Harry and Severus. For example, she might notice the strange new dynamic between them and try to use her intelligence to uncover the truth.
Some fanfictions have a plotline where Snape survives the Battle of Hogwarts and he and Harry have to deal with the aftermath together. They might have to face the wizarding community's reaction to Snape's past actions and also work on rebuilding Hogwarts. There are also stories where Harry, while still at school, starts to understand Snape's difficult position between Dumbledore and Voldemort and tries to help him in some way, which creates a whole new dynamic between them.
One interesting aspect could be the unique character dynamics. Since they are from different houses in the original story, exploring how their 'crack' versions interact can be really engaging. It might involve them in unexpected adventures or friendships that deviate from the canon.
One interesting plotline could be Severus having to take care of a deaged Harry. He might struggle with his initial dislike for Harry but gradually grow to understand him better in this new situation. For example, he could teach the young Harry some basic potions skills, which would be a unique bonding experience.
In some fanfictions, there might be a plot where Harry discovers he has a long - lost family connection to Severus. For example, perhaps they are distantly related through some ancient wizarding bloodline. This discovery could lead to a whole new dynamic between them, with Harry seeing Severus in a different light and Severus feeling a sense of obligation towards Harry.
Another plotline could involve Severus struggling with his own emotions towards Harry. On one hand, he has his long - held grudges against James Potter, Harry's father. But on the other hand, he has a sense of duty to protect Harry. This internal conflict could drive many of the story's developments, like how he interacts with Harry on a daily basis, whether he is strict or lenient, and how he deals with Harry's questions about his parents.
One interesting plotline could be Severus taking on a fatherly role to protect Harry from the dark forces at Hogwarts. He might use his knowledge of potions and magic to keep Harry safe.
One interesting Severus Snape crack fanfiction could be 'Snape's Misadventures in the Muggle World'. It humorously portrays Snape trying to navigate modern Muggle technology and culture, like struggling with a smartphone or being baffled by fast - food restaurants. Another might be 'Snape's Secret Talent for Dance' where he is somehow forced to participate in a wizarding dance competition and his stiff personality clashes with the flamboyant world of dance. There's also 'Snape and the Invisible Cat' which involves Snape being followed around by an invisible cat that only he can sense, causing all sorts of chaos in Hogwarts.
Some fanfictions have a plotline where the OC is a healer who is called to Hogwarts to deal with an epidemic of a magical illness. Snape is initially skeptical of her methods, but as she starts to make progress, he becomes more interested in her work and in her as a person. This kind of plotline allows for a lot of character development for both Snape and the OC, and also shows the different aspects of the wizarding world's medical and magical practices.
One interesting plotline could be Snape and Harry having to work together on a secret project for Dumbledore. They start off distrusting each other but as they face challenges, they gradually become friends. For example, they might be researching a powerful dark magic spell that Voldemort is after, and in the process, they learn about each other's past traumas and start to empathize.