One popular fanfiction might be 'The Adventures of Caboose and Carolina'. It could focus on their teamwork and how they overcome challenges together in the Red vs Blue universe. Maybe it shows Caboose's innocent yet powerful nature interacting with Carolina's more serious and skilled persona.
First, study their characters. Caboose is a bit goofy but has a lot of heart and strength, while Carolina is a tough fighter. Start with a simple idea, like them going on a rescue mission. Then, build the plot around their personalities. For example, Caboose might accidentally trigger some alarms but then save the day in his own way.
Well, it really depends on the size of the fan community. Red vs Blue has a decent following, and if the fanfiction manages to capture the essence of both the Caboose character and the Freelancer concept in an interesting way, it could be fairly popular within that niche. But overall, in the grand scheme of all fanfiction out there, it may not be as well - known as some of the more mass - market ones.
It's probably the combination of the beloved Caboose character from Red vs Blue and the Freelancer concept. That's a unique blend that can offer new and interesting storylines.
One common theme is the exploration of Caboose's innocence in the context of love. Since Caboose is a rather naive character in the Red vs Blue series, fanfictions often play with this trait when it comes to his romantic relationships. Another theme is the idea of unexpected love. Given the chaotic and often comical nature of the Red vs Blue world, Caboose finding love in unexpected places or with unexpected characters is a popular plot point. Also, the theme of loyalty within love is often present, as Caboose is a very loyal character in the original show.
Well, one interesting aspect could be the unique character development of the caboose. Maybe it shows how the caboose's strength is portrayed in different scenarios, like in battles or challenges within the 'Red vs Blue' universe.
In this fanfiction, the caboose could get angry if it has a goal or a dream that is constantly being thwarted by the red vs blue conflict. Let's say the caboose wants to bring peace between the two sides but they keep ignoring its efforts. It tries to communicate but they just laugh at it or don't take it seriously. So all these rejections and lack of respect make it angry.
You can try searching on fanfiction platforms like Archive of Our Own (AO3). It has a large collection of fanfictions for various fandoms, including Red vs Blue. Just use the search bar and type in 'Red vs Blue Church x Carolina' and it should show relevant stories.