A common trope is the 'protective Reid'. In many fanfictions, he becomes very protective of the reader. This could be because of his job and the dangerous situations they might get into. The 'roommate' trope is also seen quite often. They start as roommates and then feelings start to develop between them. It's a great way to create a close - proximity situation for the relationship to grow.
One popular trope is the 'genius and the normal'. Since Spencer Reid is a brilliant genius, it's common to see stories where the reader is an 'ordinary' person who is drawn to his intelligence. Another is the 'hurt/comfort' trope. Reid has been through a lot in the show, so fanfictions often have the reader comforting him. For example, after a tough case.
A common trope is the 'hurt/comfort' one. For example, when Reid is in danger during a case, Morgan is always there to save and comfort him. It shows their deep bond. Another popular trope is the 'partnership in crime' sort of thing, where they work together to solve a mystery that others can't.
One of the most popular themes is solving mysteries together. Since Reid is a genius profiler, having the reader character be involved in the crime - solving process creates an exciting dynamic.
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.
There are quite a few amazing Spencer Reid x Reader fanfictions. 'A Chance Encounter' is a really nice one. It starts with a simple encounter between Reid and the reader and then develops into a deep and meaningful relationship. The author does a great job of capturing Reid's personality. 'Love in the Shadows' is also worth reading. It has a bit of mystery in it as the relationship between the two unfolds while they are dealing with a case together.
The theme of mystery often shows up. Reid's job involves solving mysteries, so in fanfiction, the meeting might be part of a larger mystery or lead to one. Friendship is a theme too. Some fanfictions explore the idea of a platonic relationship starting from the first meeting. And there's also the theme of Reid being a bit of an enigma, with the main character trying to figure him out from the moment they meet.
One common trope is the 'stranger in Middle - earth' where the reader is from our world and somehow ends up in Middle - earth and meets Bilbo. Another is the 'unlikely pair' trope as Bilbo is a hobbit and the reader is usually a human or some other being, so their relationship is seen as an unlikely but interesting one.
The 'Forbidden Love' trope is quite popular. Maybe Robin is from a different group or has a secret that makes the relationship with the reader seem impossible at first. It adds a lot of drama.
The most romantic moment could be when Spencer Reid reads a poem he wrote for the reader. He's not very good at expressing his emotions verbally, but through his writing, he pours out all his love. The reader is deeply touched, and they share a tender kiss.
One great 'Spencer Reid x Reader Fanfic' is 'The Unspoken Bond'. It beautifully portrays the relationship between Spencer and the reader with a lot of emotional depth. Another is 'A Helping Hand' which focuses on Spencer using his intelligence to protect the reader in a dangerous situation. And 'Love in the Little Things' shows their relationship growing through small, everyday interactions.
A good 'Spencer Reid x Reader Fanfic' should have a strong character development for both Spencer and the reader. The relationship should feel natural and not forced. For example, if the writer shows how the reader's personality complements Spencer's quirks, like his fast - talking when he's excited and how the reader patiently listens. Also, a well - written plot that ties in with the 'Criminal Minds' universe is great.