As you go throughout Usotsuki's dreams, you can find a few NPCs around. Here is a list of every character in-game.
A grey-haired girl who is both in Needle World and inside of the coffin in the White Plains. Attempting to kill her, reacts differently than some of the other characters. It takes multiple hits to kill her. If she is alive in Needle World, her coffin will appear as normal. If one has killed her, her coffin will be splattered with blood.
A young black-haired girl who resides in her own room of the The Marble Hall. Many fans headcanon her and Pholus as siblings.