I'm kicking around two ideas, and I might even combine the two.
One is just 31 standard D&D characters or NPCs. What I'm hoping to do is turn it into a project "Faces of Waterdeep." It's a group of Waterdeep NPCs, but it's in the style of Humans of New York and Dear New York. Like I'll generate the PCs and give them some backstory before I flesh them out for the booklet.
The other idea I had is similar, 31 Friendly Dragons. These are dragons who can accompany heroes on quests, or be a face in their community. Who wouldn't want a dragon for a best friend?