It could mean that Marco is a character who saves Star fanfiction. Maybe in a story, Marco takes actions to preserve or rescue Star - related fan - created stories.
Well, without reading the actual fanfic it's hard to say precisely. But generally, it might involve Marco finding Star in a difficult situation with her family. Maybe her family has some sort of strict rules or is in a conflict that Star can't handle alone. Marco then steps in with his courage and unique skills or knowledge. He could be using his own experiences to help Star break free from whatever family - related problems she's facing.
The main characters are obviously Marco and Star. Marco is the one who is going to save Star from her family situation. Star is the one in need of being saved from whatever issues she has with her family.
Well, 'chopper fanfic' is basically fan - made stories that revolve around the concept of 'chopper'. If 'chopper' is a vehicle, like a motorcycle (which is often called a chopper), then the fanfic could be about cool rides, customizations, or races involving these choppers. It all depends on what the 'chopper' in question represents in the context of the fanfic.
No, in the traditional sense, Chopper, if you mean the character from 'One Piece', is a reindeer and doesn't have the physical ability to read novels as humans do. However, in a more imaginative or fictional scenario within the One Piece world, perhaps with some magic or special ability, it could be possible, but there's no such indication in the original story.
Hard to say. It could be associated with a minor character whose background wasn't fully explored. Or perhaps it was just a random prop without a specific owner.