This week's Famitsu had a feature on Fire Emblem: Three Houses, which included an interview with Fire Emblem Three Houses’ Director Toshiyuki Kusakihara and Series Director Genki Yokota. When asked about details on the game's expansion pass, Yokota had this to share.
“The Expansion Pass is only made of side-stories. It won’t contain story content happening after the main story. We’re also planning to add new characters with it. It’ll have a lot of content, so please look forward to it.”
No details on just what those side-stories will be about was shared, nor were any specifics on characters mentioned.