Often, fanfics are created by passionate fans who want to explore different aspects of their favorite characters or universes. In the case of 'caboose is a freelancer fanfic', it could be an individual who really likes the Caboose character and had the idea to put him in the role of a freelancer. They might be part of a fan group or just a lone creator, but without more information, it's difficult to determine the exact creator.
The significance might be that it represents the end or the caboose of the story, just as it is at the end of the train. It could be a symbol of closure or the final destination in a metaphorical sense.
I'm not sure which specific 'black caboose in the back story' you're referring to. There could be many stories involving a black caboose. Maybe it's part of a railroad story where the black caboose was at the end of the train, often used by the crew for various purposes like sleeping or storing equipment.
The theme of growth is also prevalent. We see Caboose evolving as a character throughout different fanfics. He might start out as the clumsy, naive character we know, but as the story progresses, he learns from his experiences and becomes more confident and capable. This could be in terms of his combat skills, his ability to make decisions, or his social skills within the group.
One common theme is the sense of nostalgia. The caboose often represents a bygone era, and the love that develops around it is kind of like a connection to the past. For example, if two people meet near an old, dilapidated caboose and fall in love, it's like they are part of a story from long ago.
The 'little red caboose story' usually tells the tale of a little red caboose that is part of a train. This caboose is likely to be a character in its own right. It could be about how it was built, painted red, and became part of the train. There might be a story of how it gets left behind at a station by mistake one day and has to find its way back to the train. It could also involve the people who take care of the caboose, like the train conductor who checks on it regularly to make sure it's in good condition.
Well, it could be a fan - made story where Caboose, perhaps a character from a certain series, is depicted as a freelancer. But without more context, it's hard to say exactly what the plot or key elements are.
There's also 'Caboose's Heroic Moments in RvB Fanfic World'. This fanfic focuses on Caboose's heroic side and how he manages to surprise everyone around him with his unique way of doing things. It's full of action and some really cool character interactions.