The Divine Mirror (神鏡, Shinkyō) is an ancient relic which drives the sequel's plot in Warriors Orochi 3 Ultimate. Its function is based on the Chinese belief that mirrors ward evil spirits by reflecting their hideous appearance back at them.
Sometime before the first game, the mirror was used by the Heavenly Emperor to seal demons plaguing the Mystic Realm. When its surface cracked, the evil spirits trapped within it were freed and gave birth to Orochi. It was stolen by Tamamo.
During the first part of the sixth chapter, the mirror's magic traps the heroes within a replica of the dimensional world. Tamamo uses hollow duplicates of the heroes to fight their real counterparts, sowing discord among the various factions. The mystics catch onto her plot in due time. Time travel is impossible inside the mirror, so the heroes break through one of the mirror's cracks. Their escape causes the mirror to shatter and lose its powers.
Fearing that the seal placed on Tamamo may break once more, the heroes go back in time to the Heavenly Emperor's era to retrieve a working mirror. Though the heroes fail to prevent the mirror from being damaged, the Heavenly Emperor restores it once Orochi and his miasma has been banished from the vicinity. The mirror eventually seals Tamamo and is returned to the mystics.
Clearing the true ending of Ultimate allows players to participate in alternate versions of certain battles where the Divine Mirror can be used to detect impostors early within the narrative. Defeating them earns the player rare orbs for fusing weapons as well as a trophy or achievement.