Focusing on the absence of a narrator:
* Silent
* Unvoiced
* Unnarrated
* Unspoken
* Unwritten (if referring to a text)
Focusing on the opposite of storytelling:
* Listener
* Audience
* Observer
* Bystander
Focusing on the opposite of conveying information:
* Concealer
* Hider
* Suppressor
* Censor
Focusing on the opposite of describing events:
* Actor
* Participant
* Protagonist
* Antagonist
Ultimately, the best antonym for "narrator" depends on the specific context and what you are trying to express.