Another character seems from their role to represent the unexpressed thoughts of another character.
Do We Have This One?? Oh, and I am open to title suggestions. Ever have doubts deep-down about some idea of yours, and imagine them being expressed by others? This is for characters, often a form of Imaginary Friend, who seem to represent these doubts on someone else's part, as a form of foil. Perhaps character X is suppressing these doubts, or perhaps character X just doesn't want to say them out loud. But character Y, who is subtly implied to be X's internal conflict embodied, has his or her role in the story be to express them, whether this is vaguely implied or confirmed by the author. Sometimes Good Angel, Bad Angel is used as a form of this. EDIT: I am still not sure how to describe this, or even how narrowed-down this should be, so input on either might be useful.
Examples:Anime And Manga