Illyasviel von Einzbern

Illyasviel von Einzbern, often referred to as Ilya, is a young German aristocrat competing in the 5th Holy Grail War. Due to her white-blonde hair and red eyes, she is often considered an albino by fans. Her Servant is Berserker.

She traveled to Japan to participate in the Holy Grail War as a Master. Illyasviel has an angelic appearance and unsurpassed potential as a Master. She lives in a castle on the outskirts of Fuyuki City, accompanied only by her Servant and two maids. Illyasviel asks those she feels comfortable around to call her "Ilya". Her mother, Irisviel von Einzbern, fought alongside Saber and Emiya Kiritsugu during the previous Holy Grail War. In the Heaven's Feel scenario she wears what is called the Dress of Heaven, what was worn long ago by her ancestor Lizleihi Justica von Einzbern.

Role
Ilya initially appears as an enemy to Emiya Shirou. The reason she is after him is because his foster father, Emiya Kiritsugu, was a Master working for her family in the previous War, but betrayed them by destroying the Holy Grail.

In Fate, Ilya eventually ends up living peacefully with Taiga after her defeat. Notably, she is somewhat attached to Shirou, and believing Taiga to be an annoyance, she is often at odds with her.

In the Unlimited Blade Works route, she has her heart torn out by Gilgamesh and during Heaven's Feel, she aids Shirou throughout his fight and eventually gives up her body to become the Holy Grail.

In Fate/hollow ataraxia, she is one of the few people who knew what's happening since the beginning of the fake grail war.

Ilya is the main character of an alternate universe spin-off manga entitled Fate/kaleid liner PRISMA ILLYA.

Past
She is in reality a homunculus, an artificial human given life by applying sorcery to sperm cells, originally created and raised by the von Einzbern family. She is actually slightly older than Shirou, her childlike appearance being a result of a distorted growth rate. During the Heaven's Feel scenario, it is hinted that the sperm used to create her was donated by Emiya Kiritsugu (it is confirmed in the novel Fate/Zero), making her his biological daughter and Shirou's step-sister. Her personal interest in Shirou seems conflicted, due to the fact that Kiritsugu, whom she had loved as her father, remained in Japan as Shirou's guardian after betraying her family by destroying the long-sought Grail. The von Einzberns then trained Ilya harshly in order to groom her as the next vessel for the Grail, and a Master who would finally bring the Grail to the von Einzbern family. Ilya, with her mother dying during the Grail War and her father abandoning her shortly after, became angry with Kiritsugu, and consequently, Shirou. She feels that Kiritsugu abandoned her for Shirou, and is jealous of Shirou for that. However at the same time, she also feels very close to Shirou for his relationship with Kiritsugu.

The von Einzbern, one of three families of sorcerers involved in the Holy Grail War (the others being the Tohsaka and the Makiri/Matou), were responsible for creation of the vessel which the souls of the defeated Servants would go into, while the Makiri created the system of Masters and Servants and the Tohsaka supplied the land which became Fuyuki City. As such, Ilya was prepared by her family to act as a living vessel for the Grail.

In Fate/Zero, the process of the Grail's creation was detailed. As each servant dies, its energy would flow into her artificial body. When six servants die, her body would be destroyed and give birth to the Holy Grail. Thus, by having Homunculus participate in the war, the Einzbern master would never be able to make a wish even when they win. The Einzbern family is fixated on victory alone because they are the family that came up with the Holy Grail War, but never won a single war.