One common theme is the exploration of power dynamics. When a scandal occurs in the Sherlock universe with an OC involved, it often shows how power shifts between characters. For example, an OC might be in a position where they have some power over Sherlock or Watson due to the knowledge of the scandal. Another theme is redemption. The OC might be a character who has made mistakes and is involved in the scandal, but then tries to make amends throughout the fanfic.
Sure. You can start by looking on Archive of Our Own (AO3). There are many talented writers in the Sherlock fandom who create OC (Original Character) - related fanfics. Just search for 'Sherlock OC Scandal' on the site and you'll find a variety of stories with different plotlines and takes on the scandal concept. Some might involve an OC getting caught up in a scandal within the Sherlock universe, while others could be about how an OC helps to uncover or deal with a scandal.
The originality. Since it involves original characters, it can take the Sherlock universe in new directions. For example, an OC could have a different cultural background or a unique skill set that Sherlock hasn't encountered before.
The unique perspective an OC brings. Since they are not part of the original canon, they can introduce new storylines. For example, an OC could be from a different culture or profession, which adds a fresh dimension to Sherlock's world.
Another theme is the mystery aspect. The fanfics usually involve some sort of mystery that both Sherlock and Irene are trying to solve. It could be a case related to Irene's past or something that Sherlock stumbles upon and Irene gets involved in. For example, in some fanfics, there are secrets about Irene's family that she and Sherlock have to uncover together. This adds an element of intrigue and keeps the story going.
Good fanfic in this genre often has an engaging plot. Whether it's a new mystery for Sherlock to solve with the help of the OC or a story that focuses on the relationships between the characters, it has to keep the reader interested. It could be something like the OC having a hidden agenda that slowly unfolds throughout the story, creating suspense and making the reader eager to find out more.
One common theme is change. Fall is a season of change, and often in these fanfics, the OC goes through some sort of transformation, just like the changing leaves. For example, they might change their view on Sherlock or their own detective skills.
One great Sherlock OC fanfic is 'The Unseen Companion'. It creates a really interesting original character who has a unique dynamic with Sherlock. The story weaves in mystery and character development really well.
Because it presents a unique adversary in Irene Adler. She's not your typical criminal, but rather a complex character who challenges Holmes. Her intelligence matches Holmes' in many ways, which makes the story more exciting.