The Ainsworth Holy Grail War (エインズワースの聖杯戦争?) of Fate/kaleid liner PRISMA☆ILLYA is a ritual started by the Ainsworth, Matou, and an unnamed family in the parallel world. Like in Fate/stay night, each of the family provided a container for the wishing device, a land with magical leylines and Heroic Spirit summoning system.
Origin
Darius Ainsworth found Pandora and Pandora's Box one thousand years before modern day. Pandora, unable to open the box in the parallel world, was rendered immortal, seeking her own death. Staying together since then, Darius eventually turned himself into a conceptual existence that overwrites the bodies of his descendants. He later created the Holy Grail War system with the other families, seeking to open Pandora's Box, but lacked a suitable Holy Grail. He had spent much time collecting Mystic Codes, magical implements, and vessels from around the world to replace Noble Phantasms or the Holy Grail. The items were simply discarded in a large pile, deemed as failures.
Differing from the Fuyuki Holy Grail War in which Illyasviel von Einzbern was born to function as the Holy Grail, the Ainsworth Holy Grail War as created for the sake of an existing Holy Grail. Finding Miyu, a person born as a completed Holy Grail, allowed the ritual to properly proceed for the first time.
Procedure
This Holy Grail War doesn't use the system of Master and Servants, but it uses a special system where a magus uses either a Mystic Code or their own body as mediums and to be granted with the powers of Heroic Spirits via Class Cards.
Mirror World
A group name for a series of pocket spaces that were created by the Class cards. They contain landscape that mirrors the one in the real world, but with no living things present, and with damage done to it not affecting the real world. Their size was originally a few kilometers in radius, but as more cards were collected, they started shrinking until the last one was the size of single building. Their name comes from the analogy that if you put two mirror opposing each other, they would reflect each other infinite number of times, and each pocket space is but a single of such reflections, a mirror image of the world.
Each Class Card was believed to be contained in a separate space, although it was shown that two cards could share a single space.
Mirror World could only be accessed by Kaleidosticks with a formed contract by opening a “Mirror Road” via a spell. After its formation a Mirror Road could immediately transfer several humans to and from the Mirror World before closing.
Supervision
The supervision of these Holy Grail Wars are again carried out by the Holy Church. However, unlike other wars, while Kirei Kotomine is still the supervisor, he stays as a mere observer and only watches events from the sidelines rather then actively participate.
Wars
First Holy Grail War through Fourth Holy Grail War
The first four Holy Grail Wars all ended in failure, notably the Fourth Holy Grail War had the worst outcome. Darius caused Fuyuki to be engulfed by darkness, causing Zachary Ainsworth, the previous Ainsworth head and the other two families to be completely destroyed. The Sakatsuki family was also wiped out with Miyu Sakatsuki being the only survivor. Darius then moved onto Julian.
Fifth Holy Grail War
The next Holy Grail War was managed by Julian Ainsworth influenced by Darius. However, unlike previous Holy Grail Wars, Julian used dolls which had the displaced souls of deceased Magi inside of them acting as the Masters, as there weren't very many people left in town. The other exceptions were Shirou Emiya and Sakura Matou who were the only living Masters. Julian then gave all of the Masters, Class Cards, to which they could install Heroic Spirits into their bodies and had them battle each other in a battle royale.
Shirou Emiya, though, was not originally one of the chosen masters, but rather chose to enter in order to save Miyu Sakatsuki who had been captured by Julian Ainsworth. After gaining the fake Archer card from Sakura and becoming able to install the soul of his future self, the Heroic Spirit, EMIYA, Shirou battled his way through the Holy Grail War, killing all the other masters (except Beatrice Flowerchild who was the user of the Berserker Class Card and managed to survive after their fight due to God Hand) and gaining their cards. Shirou then became the victor of the Holy Grail War and used his wish to send Miyu Sakatsuki to another dimension where she could have a share of happiness. During the time the Grail was working out to make his wish come true, Shirou restrained the true Archer Class Card user, Angelica Ainsworth, facing her with all his might and remaining energy before being ultimately beaten by Enuma Elish. After being sent into Illya's world, Miyu eventually met with Illyasviel von Einzbern, beginning the events of the Fate/kaleid liner PRISMA☆ILLYA series.
Sixth Holy Grail War
Though Miyu and the Class Cards used in the fifth war had escaped the Ainzworth's clutches, Darius was undeterred. As the events of PRISMA☆ILLYA played out in Illya's world, Darius patiently began preparations for a Sixth War, waiting for the day when Miyu would be within his reach again. While Angelica refused to use any Class Card other than her original, Beatrice was given the Berserker Magni. A second Berserker, Lancelot, would be given to a resurrected Sakura not as a participant in the war, but as a deterrent against Shirou or the EMIYA Card should either resurface.
Darius' opportunity would eventually come when Illya defeated the half-incarnated Gilgamesh Card at the Great Cavern, the aftermath of the climactic battle allowing Angelica (who reclaims the Gilgamesh card) and Beatrice to bridge the gap between worlds and re-capture Miyu, but unwittingly bringing Illya and co. to Miyu's world in the process. After confronting his newfound enemies, Darius boldly proclaims the resumption of the Sixth Holy Grail War, challenging Illya to rescue Miyu if it means consigning her world to death.
Participants
The events of the Ainsworth Holy Grail War are detailed in Fate/kaleid liner PRISMA☆ILLYA. All Class Cards from the Fifth Holy Grail War remained until the Sixth Holy Grail War. The Assassin Class Card's Hassan-i-Sabbah changes depending on the user.