Well, a common trope is the 'roommate' situation. In reader x reader fanfiction, it can lead to a lot of fun and sometimes awkward moments as the two readers live together. There's also the 'fake relationship' trope. They might pretend to be in a relationship for some external reason, like to make someone else jealous or to get into an exclusive event. And the 'reunited after years' trope is also seen often, where the two readers meet again after a long time apart and old feelings resurface.
One popular trope is the 'new in town' trope. The reader character is new to Derry, and then they meet the Losers' Club or Pennywise. It sets up a great scenario for character interactions. For example, the reader might be intrigued by the strange happenings in town and get drawn into the story.
One popular trope is the 'Forced Proximity'. For example, Masky and the reader might be trapped in a small space together, which forces them to interact and get to know each other on a deeper level. Another is the 'Mysterious Protector' trope, where Masky secretly looks out for the reader, and the reader gradually discovers this. It adds an element of mystery and intrigue to the story.
The 'redemption' trope can also be found in vanitas x reader fanfiction. The idea that the reader might be the one to bring out the better side of Vanitas. Or the 'shared destiny' trope, where the two are fated to be together for some grand purpose. These tropes add depth and interest to the fanfiction stories.
Another popular trope is 'hurt/comfort'. In Hiccup x Reader fanfiction, it often involves Hiccup getting injured during a dragon fight or some other dangerous situation, and the reader character taking care of him. This trope allows for a lot of tender moments between the two characters and can really deepen their bond. It also shows the caring side of both characters, with the reader being nurturing and Hiccup being vulnerable yet trusting.
There's also the 'co - workers to lovers' trope, especially considering Spencer's work environment. They start as colleagues, sharing cases and experiences, and then their relationship evolves into something more romantic. This trope allows for a lot of professional and personal interactions to be explored.
One popular trope is the 'caretaking' trope. The other characters in the story, usually the main character from the original work, will take care of the sick reader. They might bring soup, medicine, and stay by the reader's side to comfort them.
One popular trope is the 'forbidden love' trope. It could be that Silver is from a different world or group, and the relationship with the reader is not allowed in some way. This creates a lot of tension and drama in the story.
The 'mystery' trope can be found as well. Grell himself is a rather mysterious character, and in Grell x Reader fanfictions, the reader may be drawn into a world of secrets that Grell holds. Maybe the reader has to figure out Grell's true intentions, or there could be some mystery surrounding their connection that unfolds throughout the story. This can add an exciting element to the fanfiction.
The 'Forbidden Love' trope is quite common. Given Castiel's angelic nature and the rules in the Supernatural world, a relationship between him and a human reader might be seen as forbidden. This adds an element of tension and drama to the story. Also, the 'Healing' trope, where the reader helps Castiel heal from his past traumas or vice versa, is often used. They support each other through difficult times, which makes for a heart - warming story.
One popular trope is the 'Shy Guy and Outgoing Reader'. Kenma is often depicted as shy and reserved, while the reader character is more outgoing. It creates a dynamic where the reader tries to draw Kenma out of his shell. Another common trope is 'Gaming Bond'. Since Kenma is a gamer, many fanfictions have the reader and Kenma connecting over video games. They might start as rivals in a game and then develop feelings for each other.