Darkfever Plague

When the oni Oni no Kuzushi was released from it's prison within the spirit realm in 1123, it used its' power to release the Darkfever Plague upon the Phoenix lands.

The plague was leathal, spread with magic from the oni's confines of a forgotten estate deep within the Phoenix woodlands, and killed many until a group of clever magistrates located and destroyed the oni.

(3E p. 17)