A leshah are like a concubine, but neither Amon nor Nine have used them for that purpose (not really “used” them either). They’re there for the gods’ amusement. Amon doesn’t care about them and the head priest created it for Nine (per Amon’s request, I can’t specify without spoiling) but since Nine’s memories are skewed he doesn’t remember and Amon would go apeshit if Nine did anything sexual with the Leshah. The leshah are meant to die young so Rue basically signed himself to an early death for Nine and Nine hates seeing people die and hates seeing the leshah die young, but hasn’t done away with the leshah because he thinks they’re there for Amon.

What is a leshah????