More will unlock as you progress. I added unlock tags at the ends of various updates so that way the people who had already played that far didn't miss unlocking those characters.
I'll be fixing that at some point. One is the River, who isn't written yet, and the other is the Harpy, who only has the 2 scenes. Dunno why they appeared as question marks... Also, I just dropped an entire new episode today. 1.3.0.3 has Season 2 Episode 3 and a couple more side scenes!
