Since all three categories share the same meaning, I think the first two should be replaced with 'Category:Main Characters', as it has the highest number of pages among the three categories. I would also be fine with using 'Category:Protagonists' instead. Bottom line is, we don't need three categories that mean the same thing. Please vote if you are eligible. Voting ends in one week.
EDIT: Per Alan's comment, this suggestion now moves to merge 'Category:Protagonists' and 'Category:Main Protagonists' (into the former title) and keep 'Category:Main Characters'.