I’m going to keep this simple.
Story: An account of what has happened.
That is to say, when you tell a story you are talking about things that have been done, that have occurred. When you are talking about what you are doing even imaginary—my emphasis—you are not telling a story. In short, even when events are imaginary the fact that they are occurring means that story can play no role in the matter. When you play a sage in an RPG you are a sage for all intents and purposes. That it’s an imaginary sage means fuck all insofar as you are doing things. The is takes precedence over the fiction.
Just remember that the fact it is fiction doesn’t make it story.