As with the other talismans, the items were already possessed by their owners; rather than being made to summon the Grail they were made to summon Sailor Saturn herself. The mirror has been seen to work for others beside Sailor Neptune as Chibiusa once used it to locate and teleport to a different location. Michiru gave Chibiusa the mirror at some point before the Dream Arc. When the Outer Senshi returned, Chibiusa teleported the mirror back to Super Sailor Neptune in order to help her fight the Dead Moon Circus.