One popular theme is friendship development. As mentioned before, their relationship has room for growth. Another theme could be the comical misunderstandings between them. Since Lucy is often quick - tempered and Charlie Brown is a bit naive, there are plenty of opportunities for misunderstandings that can be played out in funny ways in fanfic.
Some fanfics may take a more romantic turn in their relationship. However, this is quite different from their traditional portrayal. It would involve changing the nature of their interactions quite a bit. Charlie Brown's meekness could be seen as endearing to Lucy in a romantic sense, and perhaps she would start to show her affection in more positive ways rather than just through her usual tricks like the football gag.
Yes, there are likely fanfictions out there with this plot. 'The Mentalist' has a dedicated fan base, and pregnancy storylines are quite common in fanfiction. Writers might explore how Van Pelt's pregnancy could affect her work in the CBI, her relationships with the team members like Lisbon and Cho, and how it could add a new layer of drama to the overall story.
The plot could involve Van Pelt struggling to balance her pregnancy with her demanding job at the CBI. Maybe she has to deal with difficult cases while also dealing with morning sickness and doctor appointments. There could also be some drama within the team, like some members being overly protective or others worried about her ability to perform her duties.
Sure was! 'The Peanuts' was a beloved comic that captured the hearts of many. It featured characters like Charlie Brown and Snoopy and had a wide following.