The Sidekick and the Skeptic represent the conflict between confidence and doubt in the Story Mind. The Sidekick is the faithful supporter. Usually, a Sidekick is attached to the Protagonist. Sometimes, however, they may be supporters of the Antagonist such as Renfield to Dracula.
This gives a good clue to the way we should look at functional characters: The purpose of the Sidekick is to show faithful support. That does not determine who or what it supports, but just that it must loyally support someone or something. Other dynamics of a story will determine who the Sidekick needs to be attached to in order to make the story’s argument, but from the standpoint of just describing the Archetypal Characters by themselves, the Sidekick faithfully supports.
The Sidekick is balanced by the Skeptic. Where the Sidekick has faith, the Skeptic disbelieves; where the Sidekick supports, the Skeptic opposes. The nature of the Skeptic is nicely described in the line of a song… “Whatever it is, I’m against it.” In the Story Mind, it is the function of the Skeptic to note the indicators that portend failure. In contrast, the Sidekick notes the indicators that point to success. The interactions between Sidekick and Skeptic describe the Story Mind’s consideration of the likelihood of success.