The Evil Eye was a weapon created by modifying a normal Rune Cannon. Normally in a Rune Cannon, the eye component was closed. In the case of the Evil Eye, this eye part was always open, giving it the ability to transform anyone hit by it into Fishmen. According to the sorcerer Simeon, the light the Evil Eye shoots out is that of a different world, effectively creating a pocket dimension. In that dimension, humans are unable to maintain their form and are transformed into Fishmen.
These Evil Eyes were normally used as destructive weapons, much like regular Rune Cannons. However, Kyril would encounter a larger Evil Eye in the Secret Patriarchal Facility that seemed to move and attack with a consciousness all its own. This Evil Eye had the ability to drain a persons strength and was connected to the Patriarchal Facility's floor in such a way that it could change the elemental properties of the floor. In the end, however, this Evil Eye would be destroyed by Kyril, removing its dangerous influence from the world.
- Gensosuikoden Kiwami Encyclopedia, page 526