To use my own characters as an example: I could easily get away with playing someone like say Salvatore the Magnificent along with Rozalin-someone who's canon interactions with her are minimal, not really interesting, or just don't have major importance. Whereas Mir kind of rules out my playing her boyfriend Croix or her arch-rival and best friend Shurelia. Characters like Precure mascots or Servant Berserker have been brought up previously and allowed on the grounds that they are less characters in their own right.

So uhh. I guess we would frown somewhat on Medic and Heavy being done by the same person? :| It's a case-by-case thing.