i was wondering just who is the main character of the series... coco or bart? who has more appearance in the manga?

They're both pretty evenly shown. It's a bit difficult to figure out who the main character is...
Barts is the captain, but Coco is the titular character...
Also, I would say they're both pretty evenly split in terms of screentime.
Coco seems to have a larger impact on the story, but Barts tends to be on display more for fight scenes.

Really, though... it seems to be more about the crew as a whole and their adventures.

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Personally, I see it as: Bart is Coco's mentor, and the story is about how these two separate people(actually how the entire crew) have come together, and started their adventure/life as strangers to whatever it is their relationship is. As vigorousjammer said, they are both very well represented in the manga, with similar screen times. Sometimes it focuses on Bart and other there's more focus on Coco. But since the title has Coco in it, I'd say the main character is Coco.

Resurrecting a thread which has been dead for almost 8 years

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