Whatever happened to the possibility that the fantasy narrative was the primary one? EP7 talked about Yasu's fascination with the idea of a mystery being a duel between a human detective and a magical witch. What stops her from writing a fantasy story about a witch who likes creating locked room howdunnits that don't require magic? Then you can stop trying to force silly motives on Piece Yasu, who doesn't exist, and neither the mystery nor the fantasy gets thrown out.