You can try fanfiction websites like Archive of Our Own (AO3). It has a large collection of fanfics, and you can easily search for 'red x vincent' fanfics there. Just use the search bar and type in the relevant tags.
There's also 'Red and Vincent: A New Chapter' which delves into a different scenario. In this fic, they are thrown into an alternate universe where they have to work together to solve a mystery. The way the author portrays their interactions and how they grow as characters is quite engaging.
I really like the fanfic 'Vincent's Hidden World'. It delves deep into Vincent's mysterious side and how the reader character slowly uncovers it. The descriptions in this fanfic are so vivid that it's easy to get lost in the story. It also has some really sweet and tender moments between Vincent and the reader.
A common theme could be friendship. The fanfics might explore how vincent and scott become friends, what they do together, and how they support each other.
A good 'vincent x reader fanfic' should have a strong characterization of Vincent. His unique traits, like his mysteriousness, should be well - portrayed. Also, the relationship between Vincent and the reader should develop in a believable way. For example, it could start from a chance encounter and gradually grow into something deeper.
A frequent theme is the struggle between good and evil. Vincent, with his sense of justice, and Sephiroth, with his darker tendencies, create a dynamic where this struggle is often at the forefront. Also, the theme of identity is common. Both characters have had their identities shaped by their pasts, and fanfics often explore how their relationship helps or hinders the discovery or re - discovery of their true selves. For example, in some fanfics, their interactions lead to a new understanding of who they are meant to be.
One common theme could be friendship. They might explore how Vincent and Cloud become friends, support each other through tough times. Another theme could be adventure, like they go on some sort of journey together.
Adventure could also be a theme. Maybe they go on a journey together in the fanfic, facing various challenges and growing closer as a result. It gives the writer a chance to develop their relationship in different settings.
A very interesting one is 'Beyond Duty'. In this fanfic, it shows how Vincent and Gil's relationship goes beyond their respective duties in the Pandora Hearts universe. It has a lot of character development for both of them and shows how their bond can withstand different challenges and trials.
Since I'm not entirely sure what're l x' refers to in 're l x vincent fanfic', it's hard to say for sure. But in general, a Vincent fanfic might be unique depending on how the author interprets his character. If it delves deep into his backstory, motives, or relationships in a way that the original source material doesn't, that can make it stand out.