Illyasviel von Einzbern (Fate/Stay Knight)

Illyasviel von Einzbern is one of the main heroines from the Fate franchise.

Illya is the Master of Berserker in the Fifth Holy Grail War. She is the daughter of Kiritsugu Emiya and Irisviel von Einzbern, both whom participated in the Fourth Holy Grail War, and the adoptive older sister of Shirou Emiya.

Appearance
Much like the other Einzbern homunculi, Illyasviel has crimson eyes and long white hair. Similar to her mother, Irisviel, Illya also bears a genetic resemblance to her ancestor, Justeaze Lizrich von Einzbern, who was responsible for the formation of the core of the Holy Grail. She wears a collared, purple long-sleeved shirt with a light purple scarf to match, a long white skirt and purple boots.

Though Illya was born through natural means, her body has been heavily modified before and after her birth to maximize the magical circuits in her body, making her the ultimate homunculus and a refined vessel for the Holy Grail. As a result of the modifications to her body, her physical body develops slowly and her father, Kiritsugu Emiya, correctly assesses that her physical body will not develop secondary sexual characteristics. By the time she is eight years old, Kiritsugu notes that his Walther rifle is heavier than Illya is. A decade later, when Illya meets Shirou Emiya, she still looks as though she's a young girl rather than a young woman.

Personality
Illya is cheerful and outgoing, upbeat and generally exhibits a positive attitude. Possessing a friendly demeanor, she is easy to talk to and tends to be playful and mischievous. Deep inside, however, Illya is lonely as she has no friends her own age to play with and is often stuck inside the Einzbern castle honing her magecraft. She asks those she feels comfortable around to call her "Illya".

Illya's personal interest in Shirou is conflicted due to the fact that Kiritsugu, whom she loved for he was her father, remained in Japan as Shirou's adoptive father after betraying her family by destroying the long-sought Grail. She feels that Kiritsugu abandoned her for Shirou, and is jealous of Shirou for that. When she first meets Shirou, she considers him as something of an older brother. Though he is distrustful of her at first, he comes to like Illya, seeing her as a little sister. However at the same time, she also feels very close to Shirou for his relationship with Kiritsugu. As such, she becomes very affectionate and clingy towards him (like a younger sibling would) when Berserker is defeated, much to Saber and Rin's annoyance.

It can be said that Illya gets her outward personality from her mother. Like her mother, she is kind and has the qualities of a child. However, she also has a measure of her father in her, as she can be callous and kill others without remorse. She is also unstable.

Abilities
Illya has unsurpassed potential as a Master amongst all Masters past and present. 70% of her body is composed of Magic Circuits. They are also her Command Spell and show themselves as a red pattern all over her body when she generates magical energy. The power of her Command Spell is strong enough to control Berserker who can disobey normal Command Spells. Her Command Spell is carved all over her body, and the number of her Magic Circuits overwhelms that of a typical magus. These factors and many more make her almost a vessel that exists to win the Holy Grail War. Illya has an unlimited supply of mana, thus allowing her to control Berserker without too much difficulty. Still, she suppresses the rank of Mad Enhancements to make it easy to control him when out of combat.

As a Mage, she is a top mage in Fuyuki, if it's at the land that houses the Greater Grail. Still, first-class mages would follow the "since she's a child of nature, just cut her off from the land first" plan, so it's not like she's invincible. Kayneth El-Melloi Archibald and Tokiomi Tohsaka may be able to best her in a magic duel.

Similar to the wire construct wielded by her mother, she is able to make a familiar from her hair. The name of the technique is Engel Note: Angel's Poem. The bird's name is Storch Ritter: Knight of Stork. The Ibis that shoots bullets is Zelle (German for "cell"), and she can also transform them into a Degen (German for "épée"). They are autonomous beings that defend her and pursue targets automatically, strong enough to defend against Rin's Gandr shots, fast enough to dodge them, and shown to be able to fire small blasts of magical energy capable of easily shooting through them. They each generate a considerable amount of magical energy, and Rin compares each to a "miniature magus." She can easily create up to four without any issue, and she can change their shape into swords.[16] Illya posesses Mystic Eyes of Binding which she used to capture Shirou. Though she says her Mystic eyes aren't that powerful.

Vessel of 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.

As a vessel of the Grail, Illya's body can only take up to 4 servants and if she absorbs the fifth servant, she wouldn't function as a human any longer.

Being the vessel of the Grail, Illya is able to wear the Dress of Heaven. The garment allows for the materialization of the soul and is the pinnacle of the Third Magic the Einzbern family seeks to recover through the Holy Grail Wars. She dons the Dress of Heaven during the Heaven's Feel scenario, albeit in an incomplete form of the Third Magic, to assist Shirou in completing their father's mission to stop Angra Mainyu and obliterate the Holy Grail.

Trivia

 * In the first Popularity polls of Fate/stay night in 2004, Illya was ranked 5th.
 * In the second Popularity polls of Fate/stay night in 2006, Illya was ranked 8th.
 * In the Type-Moon's 10th Anniversary Character Poll, Illya was ranked 17th.