Kanna's mirror (神無の鏡) had the ability to control others by stealing their souls. However it could not steal the souls of people with powerful objects, such as Kaguya. Also, the mirror could be overwhelmed with such a soul as Kagome's soul or Kikyō's incarnated soul. It could show whatever the Saimyōshō were seeing or show Kanna what was being reflected on a mirror-like surface. It could also reflect almost any attack back at the sender. It could repel the Kaze no Kizu, but not a Sacred arrow as they were powered by soul and thus would be swallowed into the mirror.
The mirror could also summon a glass demon. The demon could copy the abilities of the one it reflected. When Kanna summoned the Glass Demon, she could create a shadow of her mirror to shoot rays of light to her challenger. If something was sent into the mirror's shadow, the mirror itself may break, as Kagome believed. However, any damage the glass demon would receive went to Kanna herself, which made it a walking Voodoo doll.