The 'fish - out - of - water' trope is also popular. Since Stranger Things has such a unique setting, Steve's little sister might be new to the whole Upside Down situation. So she has to learn quickly about the threats and how to survive. This trope is often used to show her growth from a naive girl to a strong, self - reliant young woman.
Another trope is the little sister having some sort of special ability. Maybe she can communicate with the creatures from the other dimension, or she has some psychic powers that help in the fight against the bad guys. It adds an extra layer of intrigue to the story. In a lot of these fanfics, this special ability also causes some tension between her and Steve as he tries to keep her safe while she wants to use her powers for good.
A popular trope in these fanfictions is the 'romantic time travel' trope. Steve may travel through time and end up falling in love with a character from a different era. This can add a whole new layer of drama and emotion to the story. Also, the 'time loop' trope is seen sometimes. Steve gets stuck in a repeating time loop and has to figure out how to break it while also dealing with the events in the Stranger Things world.
I read a fanfic that was centered around Steve's little sister falling in love with one of Steve's friends. It was a really cute story. The author did a great job of showing the initial awkwardness, the secret glances, and then the development of their relationship. It also had some really sweet moments between Steve and his sister as he tried to be the protective big brother while also realizing his sister was growing up.
The theme of family can also be present. Maybe the female character comes from a broken family and finds a sense of family with Steve and his friends. Or perhaps she has a big family and Steve gets drawn into that family dynamic. These themes help to create rich and engaging stories in female Steve Harrington fanfiction.
One common theme is the shock and adjustment. Since Steve is male, the idea of him being pregnant is quite out of the ordinary in the context of the show. So, there's often a lot of focus on how he comes to terms with it. Another theme could be the support or lack thereof from his friends and family. Some stories might also explore the medical aspects in a fictional way, like how a male pregnancy could even be possible in the Stranger Things universe.
One common theme is physical injury. Since Steve is often in the middle of dangerous situations in the Stranger Things universe, fanfictions often explore how he deals with getting hurt, like broken bones or serious wounds.
One great Steve Harrington sick fanfiction is 'When Steve Took Ill'. It shows how his friends rally around him when he suddenly gets a bad fever. It's really heartwarming to see Dustin especially taking care of him, bringing him soup and making sure he takes his medicine.
You can start by looking on fanfiction.net. It has a large collection of Stranger Things fanfiction, and there are likely quite a few that involve Steve Harrington being sick. Just use the search bar and type in 'Steve Harrington sick' and you should get some results.
I highly recommend 'The Adventures of Steve Harrington'. It's a fanfiction that takes Steve on a wild journey outside of Hawkins. He gets to experience different cultures and meet all kinds of people. It's a really fun read as it shows a different side of Steve that we don't often see in the show. There's also 'Steve Harrington's Hidden Talents' which uncovers some really cool skills that Steve has been hiding all along.
One common trope is the over - protective Peter. He's always worried about his sister getting involved in his dangerous superhero life. For example, in many fics, he'll try to keep her away from any situation that might put her in harm's way.
Redemption is also a big theme. Billy, in particular, has some rough edges, and fanfics like to explore his journey towards redemption, often with Steve playing a role in that process. And of course, there's the theme of brotherhood. They can come to see each other as brothers in a way, supporting and protecting one another.