Sella is a Homunculus created by the Einzbern family, the product of a hundred different kinds of alchemy. She was amongst failures in the creation of the Holy Grail and originally she was meant to be scrapped, but she was given a new life as Illya's maid and teacher.
While she was made on the basis of the same shape as Leysritt, Sella was made as a pure homunculus two years ago with normal alchemy. Unlike Illyasviel and Leysritt, Sella is not a miracle of the Einzbern family, but a homunculus with perfect efficiency.
Despite her appearance, she is only about two years old. She usually wears a maid outfit with a hood that makes her appear almost identical to Leysritt; in casual clothing, she is revealed to have long pale hair, a characteristic of Einzbern homunculi.
Sella is highly protective of Illya, whom she loves and cares for deeply, and thus is very suspicious of Shirou Emiya.
Despite her apparent coldness to everyone but Illya, Sella is actually rather fickle and insecure, particularly about her body, and Leysritt and Illya often tease Sella for her harsh personality. Unlike Leysritt's difficulty expressing herself, Sella has clear emotions and does not hesitate to show her displeasure towards Shirou.
She tends to throw away her humanity in order to protect Illya, but she is unusually friendly to plants and animals. She usually distances herself from humans and prefers to take care of the flora and fauna of the castle.
As Illya travels to Fuyuki city for the Fifth Holy Grail War, she brings along her two maids Leysritt and Sella. Sella is in charge of the management of the castle courtyard, she tends the flower bed to establish hope for Illya there.
Unlimited Blade Works
Her role is expanded in the anime adaption. Sella disapproves Illya when she spared both Shirou Emiya and Rin Tohsaka when she returned after their first encounter. Sella complained to Illya that she could have defeated both of them easily. She believes Illya should at least killed one of them, upon revealing Berserker's God Hand Noble Phantasm. Sella realizes that Illya has pity for Shirou.
When Rin and Shirou went to the Einzbern territory to seek an alliance. Sella was against the idea to invite them and insist Illya as the lord of the castle, should drive them away. Sella lectured Illya that she should act more like the Einzbern princess and should send out invitation, and throw an evening party, in keeping with proper decorum. Sella sighs as Illya orders both her and Leysitts to capture both of them. She and Sella found Shinji Matou in the castle's garden. Sella compares Shinji to a harmless fly and decides to deal with him before capturing Shirou and Rin. Sella threatens Shinji to either jump off the roof and flee or be slain by Leysritt's halberd. As they prepare to kill him, they were interrupted by Gilgamesh. Sella instantly felt threatened by Gilgamesh's presence and Sella orders Leysitt to escape. Sella refuses to allow Shinji and Gilgamesh to pass as she is determined to protect Illya. However Leysritt was murdered as Gilgamesh fired his weapons. After the battle, Sella was impaled with several swords and was heavily injured. Sella was determined to not let Gilgamesh go near Illya, as long as she draw breath. She was decapitated by him.
Fate/kaleid liner PRISMA☆ILLYA
Leysritt and Sella both appear in Shirou's route. Sella, Celebloomers and Leysitt arrived in Fuyuki City. Sella informs Celebloomers about the preparations have been made for her press conference. As they went to the conference, nobody was there and Sella ask if Leysitt has informed the Japanese government about their arrival. They encounter both Shirou and Shinji, Shinji tells Shirou about Celebloomers being the Capsaba champ who uses the orthodox financial-power style, famous for annihilating her opponents with a deck put together by using money.
After Shirou beats Celebloomers, Sella tries to comfort Celebloomers to not be discouraged. However Sella would be grateful if Celebloomers would take this as an opportunity to grow out of this worthless game. When Gilgamesh presented Galactica Saber Final Edition, Celebloomers collapsed and Sella was concern for her well being.
She appears in Berserker's First Errand episode 5 where she drags her Leysitt back home when Leysitt was secretly following Berserker. She appears briefly in the last episode of Carnival Phantasm where she was talking to Kohaku.
She was briefly mentioned in Leysritt's story in Fate/unlimited codes, where a weakened Illya tells Leysritt to escape with Sella.
The ability of her body is inferior to others, but she makes up for it with superb magic circuits. As a magic teacher, she is superior, but as she is a fragile homunculus, Sella is unsuitable for battle. She can use magecraft to make herself unnoticeable to people who are not magus.
Creation and Conception
In early drafts, the caretaker of Illya was a tuxedo-wearing German man; someone akin to the wonderful man who nagged at Shirou and Rin incessantly. Sella made her appearance because some artistic director insisted on it and made a huge scene about it.
- In the first Popularity polls of Fate/stay night in 2004, Sella was ranked 30th.
- In the second Popularity polls of Fate/stay night in 2006, Sella was ranked 22nd.
- In the Type-Moon's 10th Anniversary Character Poll, Sella was ranked 149th.
 Fate/complete material II: Character Material - Characters: Sella, p.112
Character Data 022
Affiliation: Illya's Maid
Three sizes: B75/W58/H79
Image Color: White (Blue)
Talents: Magecraft, Home teaching
Likes: Providence, elegance, Sweet things (like cheap)
Dislike: Certain strangeness
Worst enemy: Leysritt
セラ - 魔術師として優れた素質を有するイリヤの教育係
Character Data ０２２
- Fate/hollow ataraxia - Other - Einzbern Castle - Ghost Gossip Glamorous
 Fate/complete material II: Character Material - Characters: Leysritt & Sella, p.113
Nasu Kinoko & Takeuchi Takashi • Character Discussion
Leysritt & Sella
>The catalyst for Leysritt and Sella's birth
Takeuchi: I wanted a maid duo!
Nasu: We had this conversation countless times, and every time I told him it wasn't going to happen.
Takeuchi: I won.
Nasu: Yes, I admit it... I gave in to his persistence. So anyway, when it came to throwing maids into the "stay night" mix, Illya's house was the only one that really made sense. But I made sure to tell Takeuchi that I wanted the "serious business" nun-type maids for a prestigious house of mages like Einzbern Castle. It didn't take long for Takeuchi to bring me these designs, and I approved them on the spot.
Takeuchi: I had quite a bit of fun designing these characters, as I'd never worked on a Nightingale-esque character before. I was also happy that we were adding more stoic characters.
Nasu: Ha! You've got some serious issues, my friend. At any rate, Leysritt and Sella pretty much don't do anything in "stay night". We did have the whole "Dress of Heaven" thing, but I didn't see a point in bringing that into "stay night". I expanded on it a bit in "hollow" instead.
>The presence of Leysritt and Sella
Nasu: The fact that they don't possess particularly unique traits is what makes them unique. Of the many servants assigned to Illya, these were the two selected to take care of her during the Holy Grail War. The other maids working at the main Einzbern house are also homonculi, but they are not allowed to speak freely and aren't even treated like humans. Leysritt and Sella were the only ones who were permitted to speak with Illya back at the main Einzbern house. The other homonculi are mass-production models who wordlessly go about their duties.
>Leysritt and Sella roles
Nasu: Both Leysritt and Sella have quite a few appearances in "hollow" but they were limited to a narritive role for the bad endings in "Fate". At the initial concept stage, the only details we had hammered down about these two maids were their names, their general roles (powerhouse/teacher) and which one would become Illya's Dress of Heaven. We only expanded on these characters when we decided to go ahead with "hollow". Normal homonculi are mostly emotionless like Leysritt, so that illustrates what a unique case Illya is. Leysritt was created as a sample of Illya, and Sella was allowed to live only because she was useful as Illya's tutor. That's about the extent of the specifics we initially had for these characters. When I started writing Sella's part in "hollow", however, she quickly became one of my favourite characters. I like Leysritt too, of course. By the way, I think Sella is the only real tsundere character in "Fate". (laughs)
Takeuchi: Huh? What about Rin?
Nasu: She's more like a bossy smartypants, which may seem similar to a tsundere in some aspects, but they're totally different things.
奈須 きのこ＆武内崇 • キャラクター別対談
 Fate/side material - Encyclopedia: Illya's Maids [Others], p.055-56 [T]
Illya's Maids [Others]
The maids serving Illya.
These maids made their appearance because some artistic director insisted on it and made a huge scene about it.
Sella was responsible for Illya's education, while Liz was Ilya's bosom buddy with whom she talked to.
By the way, did you know the secret that Liz had one of the biggest sets of breasts in Fate?
Basically they were failures in the creation of the Holy Grail. Originally these homonculi were set to be scrapped, but were given new lives as caretakers of Illya.
Here were some trivia. In early drafts, the caretaker of Illya was a tuxedo-wearing German man; someone akin to the wonderful man who nagged at Shirou and Rin incessantly.
- Fate/stay night - Heaven's Feel route - Day 06: beautiful (I) - Winter castle - Ilya (II)
- Fate/hollow ataraxia - Other - Einzbern Castle - Memory
 Fate/complete material III: World material - FAQ with Nasu: Holy Grail War, p.131
Q: What is Illya’s capacity as a Grail?
Q: What is Illya’s capacity as a Grail? Hypothetically, if the Einzbern won the War, Illya absorbed the other 6 Servants besides Berserker, and had some shred of human will left, could she still don the Dress of Heaven and initiate the Grail ritual?
A: That’s what Liz and Sella are for. Illya can only take up to 4 - I would think that absorbing a fifth Servant wouldn’t allow her to function as a human any longer.
- Fate/stay night [Unlimited Bladeworks] - Episode 4: "Finding the Will to Fight"
- Fate/stay night [Unlimited Bladeworks] - Episode 14: "Princess of Colchis"
- Fate/hollow ataraxia - 10/11 - School - School maid