Tokoroths! They are very young children stolen from their families, enclosed in a cave, fed only rotting bat meat. Their teeth, fingernail, and toenails are filed to a point. They are kept like that until they have forgotten even the face of their mother. Then a demon is trapped inside of them. They then do crazy-evil stuff, at the bid of their creator. Renn is often said to have a "sharp-toothed grin", which is fine, until in Outcast Seshru reveals that she was preparing Renn to be a tokoroth, until Saeunn saved her as a baby... That just makes it darkly serious.
If your three souls are scattered after death, you might return as a prehistoric zombie.
Seshru, Thiazzi, and Eostra. The demon bear. Eostra's dogs, especially when they attack Renn. Eostra's owl.
The non-consensual tattooing scene in Soul Eater. Oddly rapey for a children's book.
