Some fanfictions focus on the redemption aspect of Snape through his relationship with Harry. In these, Harry might see the good in Snape that others overlooked. There could also be themes related to secrecy and the forbidden nature of their relationship, given Snape's role as a teacher and Harry's status as a student.
One popular theme is the exploration of their complex relationship. Given Snape's often harsh treatment of Harry in the original series, fanfiction might explore how they could overcome that. Another theme could be the idea of redemption for Snape through his relationship with Harry. Also, some fanfictions might focus on their shared experiences in the wizarding world, like dealing with Voldemort's threat from a different perspective than in the books.
Some fanfictions focus on the theme of love. It could be a platonic love where Snape becomes like a father figure to Female Harry Potter. Or it could be a more romantic love, exploring the dynamics of an unexpected relationship. Also, the theme of self - discovery for Female Harry Potter is quite popular. With Snape's guidance, she might discover new aspects of her magic and her identity within the wizarding community.
Another theme could be the reaction of the wizarding world. Given their history and the rather unexpected nature of such a situation, how would the likes of Hogwarts staff, Harry's friends, and the general wizarding community respond? It can create a lot of drama and intrigue.
The theme of self - discovery is also quite common. Snape is a character who has always been somewhat of an enigma. In yaoi fanfictions, his relationship with another male character can be a journey of self - discovery. He gets to know himself better, his desires and his capacity for love. And of course, the Hogwarts setting itself is a theme, with its halls and classrooms being the places where these relationships often unfold.
One popular theme is the exploration of their complex relationship in a new light. Since they have a lot of history in the original series, in gay fanfiction, it often focuses on how they might overcome past animosities and develop a deep emotional connection. Another theme could be their shared experiences at Hogwarts, but from a different perspective that delves into their unspoken feelings for each other. For example, their mutual love for magic and how that could be a bond between them in a romantic sense.
A common theme in slash fanfiction about Snape is his emotional journey. Writers often delve into his feelings of love, loss, and regret. For example, his love for Lily is a central aspect that can be explored further. Some fanfictions might show how he copes with her death over time, and how it affects his relationships with other characters. Also, the theme of his struggle between the light and the dark side of magic is often revisited, but with a new twist in the context of slash fanfiction, like how his relationships influence this struggle.
One common theme is redemption. Severus Snape is often portrayed as a complex character in need of redemption, and his relationship with Harry can be seen as part of that journey. For example, in many fanfictions, Harry helps Snape come to terms with his past actions.
Some fanfictions focus on the friendship between Severus Snape and Lily Potter. They might explore how their relationship started as friends in Hogwarts, how they shared secrets and spells, and how that friendship was slowly complicated by Snape's growing feelings and his association with the wrong crowd. There are also fanfictions that deal with the afterlife. Given the tragic end of Lily, some stories imagine a scenario where Snape meets her again in the afterlife and they are finally able to have an honest conversation about their feelings and the events that transpired.
The exploration of Snape's character is a huge theme. Through time travel, we get to see different sides of him. We can see how his past experiences shaped him and how, if given the chance, he could have become a different person. It allows for a deeper understanding of his motives and actions in the original Harry Potter series.
Another aspect that fanfictions often explore is Snape's role during the different wizarding wars. Some fanfictions might show his secret missions or his interactions with other important characters during those turbulent times that were not fully explored in the original series.