Creation of Mirrors

It used to be that humans and the Rorrimi walked together. They visited each other's realms, intermarried, sent ambassadors, traded goods. The realm of the Rorrimi lies just outside our own, reachable through an empty wooden or metal frame. The Rorrimi were in love with human culture. It used to be we were in love with theirs. Until, on that final day, we came to love their wealth more. A band of humans attacked and killed ninety-three Rorrimi in their quest for riches. Outraged at this heinous act, the Rorrimi filled all frames with crystalline glass, perfectly solid and shined. And into the glass they placed a phantom being. A thing they named Reflection. An additional protectant against the schemes of man.

A sure way humans can never set foot in their realm again.