Windstriker was Miko Miyazaki's Paladin Mount. The horse was most likely a heavy war horse. Paladin mounts are Celestial creatures which appear when summoned by the paladin once per day, remaining for a period dependent on the level of the paladin. Miko was high enough level that her mount could remain most if not all of the day. Windstriker again fought the Order in their second (off-panel) battle which resulted in them being led in chains to Azure City.