Illyasviel von Einzbern

Illyasviel von Einzbern (イリヤスフィール・フォン・アインツベルン), often referred to as Ilya, is the Master of Berserker in the Fifth Holy Grail War of Fate/stay night. 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 silver 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 pistol 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.

Background
The 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.

Early Years
Illyaviel is a homunculus, an artificial human given life by applying sorcery to sperm cells, originally created and raised by the 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 insinuated that the sperm used to create her was donated by Kiritsugu Emiya, a fact that is confirmed in Fate/hollow ataraxia and Fate/Zero. She is the biological daughter of Kiritsugu and Shirou's adoptive sister.

Before the Fifth Grail War
Ilya, with her mother dying during the Grail War and her father abandoning her shortly after, became angry with Kiritsugu, and consequently, Shirou.

The Einzberns then trained Ilya harshly in order to groom her as the next vessel for the Grail and as a Master who would finally bring the Grail to the Einzbern family. Two months before the Fifth Grail war, Jubstacheit von Einzbern threw Illya into the wilderness. Illya was able to summon the Heracles with a slab of rock from a temple as a catalyst. The Einzbern cheated by gathering materials from the Greater Grail which allowed Ilya to successfully summon a Servant a full 2 months in advance. Even old man Acht was surprised by this result. Berserker protected Illya from a pack of wolves and the two bonded together.

Personality
Illya is cheerful and outgoing, upbeat and generally exhibiting 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 "Ilya".

Illya's personal interest in Shirou is conflicted due to the fact that Kiritsugu, whom she loved as 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 sees 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.

Development
Originally Ilya was planned to be one of the heroines, her route would have been part of Sakura story. Rather than only choosing to become Sakura's hero or fulfill his ideals as an Ally of Justice on the ninth day of Heaven's Feel, Shirou would have also had an option to become Ilya's hero instead. However due to the length, they thought to release Saber and Rin as Fate/stay night and Sakura and Ilya in a separate release titled "Fate/other night", but they thought it would have been too expensive. IIya's route was instead combined with Heaven's Feel because they decided to include Sakura's route in Fate/stay night.

Fate/Zero
She has a minor role in Fate/Zero, she first appeared in the beginning when she was born. Because the head of the family anticipated the possibility that Kiritsugu and Irisviel would fail to win the Fourth Heaven's Feel, he allowed Illyaviel to be born with modifications to allow her to become the Holy Grail should a Fifth Holy Grail War occur. In the Drama CD, she was born out of love between Kiritsugu Emiya and Irisviel von Einzbern. She will be Kiritsugu's reason for living when he comes back from the war.

As she grows up, she was very fond of her father which surprises Saber as Saber thought Kiritsugu was a cold person. Kiritsugu while carrying her realizes that she stopped growing. Before he leaves for the war, Kiritsugu promises to return to Illya, who promises to wait until he returns.

Illya does not remain far from Kiritsugu and Irisviel's thoughts during the war. During a brief moment of respite, Kiritsugu expresses his despair to his wife and his desire to take their daughter and flee. However, Irisviel assures him that he must continue. During the final days of the war, Irisviel's consciousness is consumed by the Grail, Irisviel requests Kiritsugu bring Illya to Japan and to make their daughter happy. However, as Irisviel becomes the Grail, she witnesses a vision of Illya fearing her own fate of becoming the Grail one day. Kiritsugu's own vision in the Grail eventually shows him destroying everyone he wants to protect, including all his loved ones, until he is finally forced to murder Illya.

Though Kiritsugu survives the Fourth Grail War, his choice to destroy the Grail rather than realize the Third Magic is perceived as a betrayal by the Einzbern. He makes multiple attempts to retrieve Illya, but he is prevented from succeeding by Jubstacheit refusing to open the bounded barrier around the Einzbern castle. With his deteriorating body, he could not find the entrance of the bounded field and he died regretting the thought of not being able to save her. Illya never knew that her father had repeatedly tried to save her and she was groomed to despise Kiritsugu for his betrayal.

Fate/stay night
Illya travels to Japan to participate in the Fifth Holy Grail War as the master of Berserker. During the initial stages of the war, she lives in the Einzbern Castle on the outskirts of Fuyuki City, accompanied only by her Servant and two maids Leysritt and Sella.

The reason Saber never mentioned Illya in the fifth grail war was that she had never asked Irisveil about her daughter’s name, and Illya’s appearance seemed physically too young for her to be Irisveil’s daughter. So, she viewed Illya as an Einzbern homunculus completely unrelated to Irisveil.

Fate
In the Fate route, Ilya initially appears as an enemy to Shirou Emiya. Unbeknownst to Shirou, his foster-father had been the Master for the previous War, representing the Einzbern family. Kiritsugu's decision to destroy the Holy Grail had been regarded as a betrayal and is the apparent reason for why Illya has decided to specifically target Shirou. After Saber is weakened after her fight against Rider, Shirou is captured by Ilya, who gives him the proposition to become her servant, which he refuses. Frustrated with his response, she orders Berserker to attack Rin, Saber and Archer, who had come to save Shirou.

Archer sacrifices himself in order to allow Rin, Saber, and Shirou to escape, by staying behind to fight Berserker despite knowing he is outmatched. He manages to take six of Berserker's twelve lives (five in the anime) before he is ultimately defeated. In order to replenish Saber's mana, Shirou has sex with Saber (or gives a part of his magical circuit to her in Réalta Nua) and they go fight against Illya and Berserker. Berserker is defeated by Saber and Shirou after the latter traces Caliburn, Saber's original sword. Without the protection of her Servant, Illya joins Shirou's household. She lives peacefully with Shirou and winds up being by Taiga. Notably, she is somewhat attached to Shirou, and believing Taiga to be an annoyance, she is often at odds with her. However, according to Archer, she has less than a year to live due to being an Einzbern homunculi.

Unlimited Blade Works
In the Unlimited Blade Works route, she has a lesser role. She introduces herself as a Master to Shirou and Rin, but since the most dangerous servant in the route is Caster, she doesn't attack them. In order to defeat Caster, Shirou and Rin decide to form an alliance with Illya. However, they arrive too late at her castle and Illya is defeated and killed by Gilgamesh after the latter rips her heart out of her body. Before dying, her past together with Berserker is fully expanded, revealing that after Kiritsugu left her, Illya went through a cruel training by the Einzberns so she could be able to control Berserker and be their representative in the Grail War.

Heaven's Feel
During Heaven's Feel, Illya does the same thing that she did in Fate: upon realizing that Kiritsugu is dead, she decides to take revenge on Shirou. She attacks Rin and Shirou by surprise and Shirou gets injured after protecting Saber. When they meet again in the park, she forms a friendly relationship with Shirou and they chat frequently in the park. She tells him about her past and about the Dress of Heaven. She also appears to be aware of the relationship between Shirou and Archer.

Illya is later attacked by Zouken Matou after Berserker is defeated by Saber Alter and corrupted into becoming one of Sakura Matou's Servants. Once Berserker is destroyed, Illya reveals the truth regarding Heaven's Feel, the Holy Grail, and Angra Mainyu, the corruption in the Grail. Together with Rin, they work together to replicate the Jeweled Sword of Zelretch, which Rin intends to wield against Sakura, who has become a second vessel for the corrupted contents of the Grail. Illya remains behind while Shirou and Rin confront Sakura, extracting a promise that they will return alive.

During Shirou's battle with Saber Alter, Illya locates the Dress of Heaven, a conceptual garment used by Illya's ancestor, Justeaze von Einzbern, during the First Heaven's Feel. Realizing that even if Shirou manages to defeat and retrieve Sakura it would be insufficient to save everyone from the Grail's destructive power, Illya intends to utilize the Dress of Heaven to protect Shirou.

If the affection score for her is high enough, it results in Sakura's True Ending (if the affection score is low, she regretfully kills Shirou resulting in a Bad End). Ilya appears using the Dress of Heaven, appearing just in time when Shirou is about to sacrifice himself to destroy the Greater Grail. She stops him and materializes her soul using an incomplete form of the Third Magic. Illya reveals to Shirou that she is his older sister and tells him that because of it, her duty is to protect him. She eventually gives her body up to become the Grail and performs Heaven's Feel on Shirou to keep him alive.

Fate/stay night Manga
In the manga version of Fate/stay night (which follows the Fate and Unlimited Blade Works scenarios), the events involving her character follow the Fate route. After kidnapping Shirou, losing Berserker and ultimately being defeated by Shirou and Saber, she ends up living happily at Shirou's house.

Fate/hollow ataraxia
Two months before of events of Fate/hollow ataraxia, Rin and Illya perform an experiment at the Einzbern Castle in Fuyuki City, using a duplicate of the Jeweled Sword Zelretch that they intend to transform into a pendant that will allow them to travel to different parallel worlds. The experiment fails and consequently leaves Fuyuki City in a state where any and all events are possible. As a result, all the Servants and Masters from the Fifth Holy Grail War, excluding Kirei Kotomine, are revived. Rin leaves for the Mage's Association soon afterward to avoid being punished for disrupting the time-space reality of Fuyuki City.

Illya maintains her cheerful yet rude attitude and is very attached to Shirou. Surprisingly, Illya is one of the few people who knows the circumstances behind the strange events of the false Grail War from the very beginning, but she does nothing about it. It is also common knowledge that she is Kiritsugu's daughter and Taiga will often ask for Shirou to take Illya to Kiritsugu's grave. Illya now understands the reasons why Kiritsugu had to abandon her and has come to terms with this.

Other appearances
Ilya has a number of small roles in Carnival Phantasm, often as a commentator in the parody versions of the Holy Grail War with Kirei Kotomine. Ilya is the main character of the Magical Girl spin-off, Fate/kaleid liner PRISMA☆ILLYA.

Abilities
Illya has unsurpassed potential as a Master. Ilya has an unlimited supply of mana, thus allowing her to control Berserker without too much difficulty. Her body is capable of holding an immense number of Magic Circuits, and she also possess the Mystic Eyes of Binding.

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, an artifact that was worn long ago by her ancestor Justeaze Lizrich von Einzbern. 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.