Dramatica

If your protagonist is following a positive change arc, the impact character or characters will represent or demonstrate the thematic truth that conflicts with the lie the character believes.

So impact character is the term coined by Dramatica authors Melanie Anne Phillips and Chris Huntley to describe what is just as accurately termed by editor Roz Morris the catalyst character.

This is the character who slams into your protagonist, catalyzes them into change, and has a major impact on their life.

So just as a reminder, in a positive change arc, the story begins with the lie the character believes, which references the comparatively limited belief or state of being in which the protagonist begins.

And the answer is not necessarily.

Although the impact character, as we're discussing it here, is specifically a truth-aligned character used by the writer to leverage change in the protagonist's arc, you can also create negative impact characters who instead align with the lie.

So similar to what the Dramatica system terms the antagonist, which is sort of an anti-mentor, a negative impact character will represent the seductive force of the protagonist's lie.

And this is a character who, intentionally or not, attempts to influence the protagonist to either maintain the lie's status quo, or in some cases, to actually regress away from the truth back to the more constrictive perspective of the lie.