At first, I thought of having five different stats for the characters, each one "opposed" to two other stats, represented in the form of a pentagram. It made sense thematically and seemed easy enough to grasp on paper; however, it went against another aspect we really wanted to experiment with: the ability for characters to evolve and heal or succumb to their traumas. This implied the need for statistics to grow, and if they had to be compared and "mathed" against one another every time the players wanted to act, this would slow down the pacing and risk turning into a chore at some point.
So rather than relying on several stat values, we kept only one: the demon strength (voice). But this also reduced the potential for characters' evolution. So what I did instead is I designed "traumas" and "hopes", specific rule-breaking abilities characters could unlock or be afflicted by as they evolved away from, or toward their demon.