A less common but still interesting trope is the 'swap universes' scenario. In this, the characters from Supernatural end up in The X - Files universe and vice versa. They have to navigate the different rules and cultures of the new world while still trying to find a way back home. It can lead to some really creative and humorous situations.
There are also a lot of 'Alternative Universe' (AU) fanfics. These can range from modern AUs where the characters are in a completely different setting, like high school or a corporate office, to fantasy AUs where they might be in a magical world. These AUs give writers the freedom to explore different aspects of the characters' personalities and relationships outside of the show's canon.
One common trope is the forbidden love between a human and a supernatural being, like a vampire. Another could be the power dynamics in sexual relationships within the supernatural world, such as an alpha werewolf and his mate. Also, the idea of soulmates in a supernatural context often features in these fanfics.
One popular X Files shipper fanfic might be those that focus on the relationship between Mulder and Scully. For example, stories that explore their early days of partnership and the gradual development of their feelings. There are also fanfics that take a different turn in their relationship, like what if they got married earlier in the series' timeline.
One popular 'r x files fanfic' might be those that explore the relationship between Mulder and Scully in alternate universes. For example, there could be a story where they meet in a world where the X - Files never existed but they still have an immediate connection.
The 'roommate' trope can also be found. Imagine Andrew and Neil having to share living quarters for some reason, like being on a special exy team training program. This forces them to interact more closely, leading to a deeper understanding of each other and the development of their relationship.
One popular trope is the 'enemies to lovers'. It could start with Abby and the reader having some sort of conflict or misunderstanding, and then gradually falling in love as they get to know each other better. Another is the 'hurt/comfort' trope, where the reader might be in a difficult situation and Abby comes to their rescue and offers comfort.
The 'adventure together' trope is quite popular. It involves the futa and male characters going on an adventure, during which their relationship develops. The 'cultural difference' trope can also be seen, especially if the story is set in a fictional world with different cultures. Here, the differences between them can create interesting plot points. Also, the 'redemption' trope, where one of them, usually the futa, might be seeking redemption and the male character plays a role in that journey.
Some fanfics use the 'redemption' trope. Bowser might start off as his typical villainous self, but through his interactions with the reader, he begins to change for the better. There's also the 'mysterious stranger' trope where the reader is new to Bowser's world and he is intrigued by this unknown entity, leading to their relationship developing.
One popular trope is the 'Training Partner' where the reader becomes Goku's training partner. They start off as someone Goku helps to improve their fighting skills, and a relationship blossoms during the intense training sessions. Another is the 'Saved by Goku' trope, where the reader is in danger and Goku swoops in to save them, which then leads to a deeper connection. There's also the 'Power - up' trope where the reader somehow gains power with Goku's help and they go on adventures together.
The 'soulmate' trope can be found in Percy x Luke fanfics as well. In this trope, they are destined to be together in some way, whether it's through a magical bond or a prophecy. This trope often adds a sense of fate and inevitability to their relationship. Additionally, the 'secret relationship' trope is used, where they have to hide their feelings and relationship from others in the Percy Jackson world.