Avalon

Avalon is the hallowed scabbard of Excalibur, the embodiment of the utopia King Arthur seeks, originally stolen from her shortly before the Battle of Camlann. It is a luxurious piece of equipment made of gold and decorated with blue enamel that seems more like a treasure to show dignity and nobility than a weapon. It was created by fairies along with Excalibur as a materialization of the collective wishes of mankind, and its middle is engraved with an inscription written in Fairy Letters to show it is not the work of man. It bequeaths limited immortality through constant regenerative simulation, as well as preventing physical deterioration due to aging. Its function as a Noble Phantasm is to completely shield its user in the domain of fairies, Avalon, the unreachable utopia that Arthur dreamed of and was said to have gone to after his death. It is the greatest protection in the world that goes beyond defending or reflecting, and actually completely isolates its user in another world. The scabbard dissipates into countless particles and immerses the user to become a "portable fortress" that shuts out all interference. Once in the Bounded Field of the tranquil domain of the fairies, the individual is shielded from all destructive interference in the physical realm, transliners from parallel worlds, and multidimensional and multiplanar contact up to the sixth. It is on the level of true magic that transcends all magecraft, and not even five current magics can overcome the barrier.

It was excavated in Cornwall at the request of the Einzberns shortly before the Fourth Holy Grail War and used as the catalyst to summon Arturia as a Saber-class Servant. It is still in pristine condition after one thousand five hundred years, though it no longer functions without a connection to its original owner. It is able to be used as a "Master's Noble Phantasm" after she is summoned. It can be disassembled and sealed inside Saber's master or someone who will constantly be close to her, such as Irisviel von Einzbern, as a Conceptual Weapon to provide them with its regenerative abilities and also allow them to supply more prana to Saber. There isn't a requirement of having a contract formed with Saber to use its abilities, but having one will provide the true benefit of immortality. The scabbard constantly provides regenerative abilities while she is close, and by making contact with Saber, injuries can heal even faster. She is also able to directly give prana to the scabbard to further the regeneration. It will not function or have any of its properties if she is unable to provide it with prana by being near its wielder. It is potent enough to heal critical wounds rapidly and restore the wielder's health. The body will reconnect itself, large missing portions of the body will be restored, and cuts will quickly heal. It is enough to keep Irisviel functioning as person, while she would normally start to break down and lose functions as a human due to her status as the vessel of the Grail. She needs to be within range of Saber to function completely normally, while her suffering increases as Saber is farther away.

It can be removed from its user at any time to be passed on to another wielder. Irisviel places her hand on her chest, concentrates prana within her on to her fingertips, and the form of the scabbard appears within a silhouette of light before finally manifesting. It is passed on to Emiya Kiritsugu, who manages to use it to use Innate Time Control, which normally shatters his bones, at double his normal level of use. It is implanted in a dying Emiya Shirou at the end of the war to save his life, and remains within him ever since that day. It is used as the catalyst to summon Saber a second time, and heals him from a number of fatal wounds after she is summoned. It is discovered during the Fate route, where he manages to use its barrier function by projecting it. It has merged with him to the point where the projection is a perfect replication without any degradation that bypasses all of the steps due to having a complete record of it. He and Saber are able to remove it from him through Projection in order to return it to her from across time.