The Holy Grail was used by Sailor Moon in the anime and manga to transform into Super Sailor Moon. Although it had different origins in the manga and anime, in both versions the Holy Grail was the item that both the Death Busters and the Senshi of the Outer Solar System were searching for, and was the item that could be used by a Messiah in order to either save the world or bring about the Silence.
In the manga, the Grail appeared when the hearts of Sailor Moon, Tuxedo Mask, and Sailor Chibi Moon came together. Its appearance broke the spell Cyprine and Ptilol had put on the other Sailor Senshi, and their hearts and power combined, allowing Sailor Moon to transform into Super Sailor Moon at the same time. At this time the talismans also resonated together in reaction to the power. Sailor Chibi Moon also received her own Grail that allowed her to transform into Super Sailor Chibi Moon.
Before the Grail appeared, Chibiusa had spoken of a picture of a beautiful jeweled grail that she saw in Neo Queen Serenity's room, and attempted to make a clay replica of it for her art class in school. Diana mentioned that the Grail contained wondrous power that could save people.
Without all of the Senshi present, Sailor Moon and Sailor Chibi Moon could not use the Grail to transform.
In the manga, the Holy Grail was eventually upgraded to form the Holy Moon Cálice.
In the anime, the Grail was formed when the three talismans were gathered together. Using the power of the Grail, Sailor Moon could use Crisis, Make Up to temporarily transform into Super Sailor Moon.
The Grail was taken and used by Mistress 9 at the end of the Sailor Moon S season and did not appear in the anime again. An unknown object similar in appearance to the Grail did appear in the Sailor Stars season, but was not used as a transformation item.
According to Christian mythology, the Holy Grail was a cup or dish used at the Last Supper by Jesus Christ which supposedly had miraculous powers. In some versions of the myth, the cup was also used to catch some of the blood of Christ after he was crucified. The Grail has since appeared in different forms in a number of literary works, including some versions of the King Arthur legend.
The toy for this item released by Bandai called it the "Rainbow Moon Cálice."