Another important aspect is her goals and dreams. If Emily is all about catching criminals, the sister could be more interested in helping people in a different way, like through social work. This would create a contrast between them. And don't forget to show her flaws. Maybe she's a bit stubborn or has a short temper, which can make her more human and relatable in the fanfiction.
One possible storyline could be the sister getting involved in one of the BAU cases in an unexpected way. Maybe she has a special skill or knowledge that helps the team solve a particularly difficult case. For example, if she's a psychologist herself, she could offer a different perspective on the unsub's motives.
One common theme is family. Since the OC is a sister, there's often exploration of family dynamics within the context of the BAU. Another theme is acceptance. The OC sister usually has to prove herself to the team and gain their acceptance. For example, in many stories, she might have an unorthodox method of profiling that the team is initially skeptical about.
A believable OC needs to have real - world experiences that shape who they are. In the context of Criminal Minds, if the OC is supposed to be a part of the action, they could have had a family member who was a victim of a crime in the past. This would fuel their drive to be involved in solving cases. Their skills should also be developed over time. Don't make them a super - human who can do everything perfectly. Let them struggle and learn, especially when working with Morgan who has a lot of experience.
Family relationships are a very common theme. Since it's about Rossi's sister, exploring how they interact as family members, with all the love, conflicts, and support that comes with it. Another common theme is mystery. Given the Criminal Minds setting, the sister might be involved in some sort of mystery related to the BAU's cases.
A common theme is family dynamics. Since it's about Tara and her OC sister, exploring their relationship, whether it's a loving bond or a more complex, strained one, is often seen.
A frequent theme in these fanfictions is the OC's hidden talents or abilities. For instance, she might have a special skill in profiling that she's been developing on her own. This theme of self - discovery within the context of the 'Criminal Minds' universe is really engaging. Also, the theme of friendship within the BAU is often explored as the OC sister forms relationships with the other members of the team like Reid or Morgan.
The theme of mystery and danger also runs through many of these fanfictions. The sister might get involved in the cases either by accident or because she has some special knowledge. This leads to her being in dangerous situations, much like the BAU team, and having to use her wits to get out of them.
One great Criminal Minds OC sister fanfiction is 'The Unseen Sister'. It adds a new character, an OC sister, into the BAU team's world in a really interesting way. The story focuses on how she copes with the challenges of the job while also having her own personal struggles.
One popular 'Criminal Minds JJ sister OC fanfiction' is 'The Unseen Sister'. It explores the relationship between JJ's sister and the BAU team in a really interesting way. The OC in this fic has a unique personality that adds a new dimension to the story.
One possible fanfiction could start with Penelope's sister arriving at the BAU unannounced. She's a bit of a free spirit, different from Penelope's tech - savvy self. Maybe she has some psychic abilities that she's not fully aware of yet. As she wanders around the BAU, she starts to pick up on the energy of the place and the people. She could have an instant connection with Reid, who is intrigued by her unique perspective. They start to have conversations about the cases from a more intuitive angle, which throws the team into a new way of thinking about their investigations.