Another theme is the power dynamic between them. Stolas is a powerful demon with a high social standing, while Blitz is more of an underdog in a way. Fanfictions may play with this power dynamic, sometimes having Blitz gain power or influence in the relationship, or Stolas learning to respect Blitz's agency more. Also, there are often themes of redemption and self - discovery for both characters within the context of their relationship in these fanfictions. They might grow and change as a result of their connection to each other.
A plotline might involve them going on adventures together outside of their usual work - related tasks. They could discover new aspects of each other's personalities and grow closer as a result. Also, there could be a plotline where they face opposition from other characters in the Helluva Boss universe who don't approve of their relationship.
The contrast between their characters. Stolas is refined and powerful, while Blitz is rough around the edges and scrappy. This creates a dynamic that fans find interesting to explore in fanfiction.
You can try websites like Archive of Our Own (AO3). It has a large collection of fanfictions across various fandoms, and there are likely many Stolas x Blitz fanfictions there. Just use the search function on the site.
Magic and the supernatural are often themes as well. Stolas has powerful magic abilities, and fanfics play with how he uses them, discovers new powers, or how his magic affects his relationships. Some fanfics also explore the origin of his magic and how it ties to his family's history.
There's 'Stolas and His Daughter'. This fanfic focuses on Stolas' relationship with his daughter. It shows his more tender side and how he tries to be a good father in the complex world he lives in. It's a heartwarming read.
There might be such a fanfiction out there. However, it could be a bit of a niche concept within the fandom. Some fanfiction writers like to explore unique and unexpected scenarios for characters. But it also might not exist because not all fans would be interested in this particular plotline. It really varies from writer to writer and the overall trends in the fan community.
A fem Harry x Charlie pregnancy fanfiction could explore different themes. For example, it could focus on the reactions of their friends and family. Maybe Harry's friends from Hogwarts are shocked but supportive. Charlie, being a dragon keeper, might have his own concerns about bringing a child into a world where his job is so dangerous. It could also show how they adapt to their new roles as parents - to - be.
I'm not sure specifically what a 'charlie x panda fanfic' is about without more context. It could be a fan - created story involving characters named Charlie and Panda, perhaps about their adventures together, or it could be a story of their friendship in a fictional setting.