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Sebastian takes on the appearance of a tall, handsome adult with black hair, red eyes, and pale skin. He typically dresses in a butler outfit, which consists of black trousers, a six-button double-breasted tailcoat, and a gray vest. He has the Phantomhive crest on his shirt cuffs and tie. He also sports a pocket watch and a chained silver lapel pin bearing the Phantomhive crest, as traditionally worn by the house's head butler.
Sebastian's demonic form has never been fully shown. Details of this form include high-heeled stiletto boots, sharp claws, glowing fuchsia irises, slit pupils, and longer, sharper teeth, with dark wings.
Sebastian is a dedicated butler to Ciel Phantomhive and upholds a strong sense of duty to his master and household. He follows and completes each order faithfully, while always ensuring that the Phantomhive house runs smoothly. He does not sleep, for demons view it as a form of luxury, and thus frequently performs tasks for Ciel at night. The manner in which he responds to Ciel's demands is quite notable; he says, "Yes, my Lord."
Despite his appearance as a courteous and excellent servant, Sebastian is actually a heartless and sadistic demon. He expresses these traits in a very passive and sarcastic manner. He is ruthless when attacking others on Ciel's orders, such as when he kicks Grell Sutcliff's face because it is the thing Grell most cherishes. His diabolic nature is also shown through his dark humor and inability to see good in anyone. At times, Sebastian can be indifferent; he had, at one point, deliberately delayed saving Ciel, for his own amusement. He thinks Ciel is a "brat," who treats his workers rudely, but has admitted that he does not dislike the butler lifestyle, despite all the troubles he goes through on a daily basis.
Sebastian views money as "rubbish" or "materialistic." He is fluent in French and Latin, enough to teach the latter. He is also knowledgeable and proficient in Deutsch (German) and East Franconian, a dialect in Southern Germany.  Sebastian has a strong and mutual distaste for Grim Reapers. He greatly favors cats, and keeps at least thirteen hidden in his closet to prevent Ciel from finding out.
Sebastian often contemplates the behaviors and attitudes of human beings. He finds humans in general to be "difficult creatures," but he adds that their struggles and lofty goals make them interesting. He is also intrigued by how seemingly insatiable they are, as they are willing to "drag others down to get what they want, even in death." 
Sebastian's real home is in an alternate world that is quite different from the human world. In particular, he mentioned that the creatures kept as pets there are in no way comparable to cats. Sebastian had briefly remarked that he met an ancient Egyptian mummy when it was alive, identified as Smenkhkare who reigned about three thousand years ago. He was also a guest at the Schönbrunn Palace from time to time. He also claims to be responsible for the spread of the Black Death that occurred five hundred years prior. In short, he muses that Ciel Phantomhive's life in comparison would feel like an instant.
Sebastian stated that, in the past, he engaged in "messily sampling every dish available," and has since resorted to only consuming "high-quality" souls. As a result, he has been apparently starving, but he declared that the "dinner" will be much better the hungrier he is.
Three years ago, he was summoned to Ciel Phantomhive when the latter was about to be sacrificed in an occult ritual. After forming the contract with Ciel and placing the seal on his right eye, Ciel ordered him to slay his abductors. Sebastian decided to adopt a "role that is best fit to serve an Earl", therefore taking a form of a butler, until Ciel completes his personal mission of revenge—that is the substance of their contract. In return, Sebastian will receive Ciel's soul. He was then given the name "Sebastian" by Ciel, which used to be his dog's name, for the duration of his duties as Ciel's butler.
Once he was finished annihilating the cultists, they went to the Royal London Hospital to meet with Ciel's aunt, Angelina Dalles. There, Tanaka gave him a watch that had been passed down from one Phantomhive butler to the next. After that, Angelina arranged for a carriage to bring them to the ruins of the Phantomhive manor. While Ciel was mourning the deaths of his parents, Sebastian reconstructed the manor.
Ciel and Sebastian then began daily life. He taught Ciel the fundamentals of an being an earl, while he learned from his new master how to be a butler fit for the Phantomhive household. He later attended Ciel's coronation as the Earl of Phantomhive, but did not observe at a close distance because he saw himself as a mere butler, not family. While they were walking, Sebastian asked Ciel if he was happy with how things were and, at Ciel's hesitation, attempted to devour him. He was stopped, however, when Ciel suddenly turned around and stated that he was determined to attain his revenge. He commanded Sebastian to be his sword and shield and bring him victory. Sebastian complied, as he was sure that Ciel's soul would be extremely delicious.
Sometime during the same year, Sebastian was summoned to Ciel's room, who complained of a wobbly tooth that was preventing him from eating his food properly. After examining it, Sebastian decided to forcibly take it out, much to Ciel's chagrin. Ciel attempted to protest against the idea but Sebastian proceeded regardless, under the impression that he was doing his young master a favor. After the tooth removal, Ciel threw an angry fit at Sebastian. Ever since, he was unwilling to allow Sebastian to check for cavities in his teeth when they started to wobble.
Jack the Ripper Arc
Curry Contest Arc
Noah's Ark Circus Arc
Phantomhive Manor Murders Arc
Ship Voyage Arc
Public School Arc
Green Witch Arc
- (To Ciel Phantomhive) "Yes, My Lord."
- (To Ciel Phantomhive) "It seems your talent for dancing is non-existent. It must be crushing, young master."
- "I am the butler of the Phantomhive family. It goes without saying that I can manage something like this."
- "I am one hell of a butler. So long as the young master possesses the 'mark of the covenant' . . . I am his faithful dog. A 'sacrifice' . . . a 'wish' . . . and a 'covenant' bind me to my master.
- "Young master. Forgive me. As butler of the Phantomhive Family, this is an unpardonable disgrace . . . I do not know how I should atone for this . . . I have been unable to prepare dinner this evening."
- "A butler begins his day early. He is the last to finish his work late at night, and the first to begin work in the morning. Such is the duty of a butler who manages the household."
- (Referring to Mey-Rin) "Why, this imbec—that is to say, housemaid. It would seem the problem no longer lies in her eyesight. Why does she fail to realize that there is something clearly wrong with her own brain and not the instructions? Word has it that the public adores silly maids. But I do not think I will ever understand it, and I have no intention of even trying to do so. I myself would like to wring her neck."
- (Referring to Baldroy) "Why this imbec—rather chef. You should talk about cooking after you have actually cooked something. I believe eighty percent of what you have managed to cook has been charcoal. The other twenty percent was hazardous waste. Save your art for you hairstyle, and cook something edible . . . otherwise . . . I wish for you to become charcoal yourself."
- (Referring to Finnian) "Why this imbec—this imbecile! How can a gardener be so clumsy? Though the saying goes, 'an idiot and a pair of scissors can both be of use,' giving this useless idiot a pair of scissors is trouble in itself. He refers to something that happened two or three days ago as being 'a while back.' The way his brain can easily cast aside a blunder of that degree . . . I have surpassed anger, and I am, in fact rather impressed."
- (About Finnian) "I have lived for quite some time, but this is my first encounter with a being from outer space. How does he expect me to respond to his beaming smile?"
- "I have had enough. In times like these, yes . . . I want to see her. A supple body, flowing black hair. I must hurry . . . to the place where she awaits me . . . to her. I find cats most agreeable. They only say (do) that which is necessary. They are quite adorable. They do not exist in my world. Pets do exist over there, but . . . they leave much to be desired."
- "I, your 'chessman,' am your 'might,' your 'hands' and 'feet' . . . you alone will decide . . . you yourself will choose . . . and for that, I shall become your 'might.' You said as much . . . 'that day.' I am merely a 'butler.' I will not cross that line. I only faithfully execute what the master orders, and answer what the master asks me. By your order . . . I, your 'chessman' . . . shall become your 'sword.' Now then . . . let us move into check, Master."
- (To Grell Sutcliff) "From the time . . . my master called me 'Sebastian' . . . that word became my covenant and christened me anew. I have been 'Sebastian' since that day. I vowed as much to the moon, you see?"
- (While stepping on Grell Sutcliff's face) "I do not enjoy being stepped on . . . but being the one doing the stepping is another story altogether."
- "Humans are easily tempted. When they are poised on the edge of hellish despair . . . and a spider's thread of salvation presents itself, they will invariably grasp it . . . no matter the manner of human."
- (To Frances Midford, about Ciel Phantomhive) "The young master has an inordinate talent for games. Consequently, he seems to over-confidently believe that he 'cannot lose.' But at times, it will be necessary for him . . . to carry himself with humility while striving for his goal. Otherwise, he will eventually trip up . . . as the place for which young master aims is not an easy one to reach. Perhaps it is not my place to say this, but . . . I would like you to be an exemplar for my master, Marchioness."
- (To the other Phantomhive servants) "Why do you three not kowtow and beg Mister Agni for the dirt under his nails? Your lives might gain a little value that way." 
- (To Ciel Phantomhive) "—Oh? What a tiny master this. You have summoned me. That fact will not change for all eternity . . . and the sacrifice that has been made will never return. Make your choice."
- (To Agni) "England or India, it makes no difference. No matter where or from what era, they are all alike . . . those beings called humans."
- (To William T. Spears) "I grew weary of indiscriminately devouring souls long ago. The more ravenous I am . . . the more delicious the dinner."
- (To William T. Spears) "My goodness. That must be quite a chore to handle alone. Still, a large number of souls . . . shall I lend you a hand?"
- (To Ciel Phantomhive) "As long as there is the contract, I will protect your life. However, if you make a mistake of your own accord, you will possibly suffer a painful experience while alive. You already know that, don't you? Any game becomes boring when it lacks thrills."
- (To Beast) "Why not forget just for the tonight? Drown in pleasure . . . and breathe sweet poison deep into your lungs."
- (To Ciel Phantomhive) "You are different from demons who are revolting and possess complex evil intent. Telling lies . . . desperately struggling, kicking down other people. Stealing the stolen, while repeating your reasons over and over. And even so, you aim for the horizon over the hills. That's why humans are interesting."
- (To Elizabeth Midford, about Grell Sutcliff) "He's just a pervert. I'm afraid it might be contagious, so please step back and stay away from him."
- (To Ronald Knox) "Young’uns these days are really so feeble. Isn't it kind of old-fashioned to just rely on your Death Scythe?"
- "How interesting... Humans will drag others down in order to get what they want even in death. What truly insatiable creatures!"
- (To Ciel Phantomhive) "Society has monsters lurking that are far nastier than a demon like me."
- (Referring to Ciel Phantomhive) "He turns his back towards the light without hesitation. That figure that charges into the abyss at a dignified pace. How beautiful and foolish."
- (To Undertaker) "That's where we differ. Exactly because 'death' is such a hopeless and definite 'end' . . . it is beautiful."
- (About Ciel Phantomhive) "Ah, my master. You're misunderstanding something. What I find most entertaining now . . . is playing the butler in my game with you. It's not behaving like a frenzied beast. However, if that's how you like me . . . I'll act accordingly. Because I'm one hell of a butler."
- "If it's your wish I will follow you everywhere. Even if your throne crumbles and your shiny crown turns to rust. Beside you as you lie, softly down, I will be. Until I hear the words, 'checkmate'."
- (To Ciel Phantomhive) "For a king to survive it's good for him to be able to skillfully manipulate the other pieces using both the knight and the queen. Beneath the throne the bodies of your pieces will pile up along with your sins. You must not lose."
- (To Claude Faustus) "Demons have eternal life. We've grown weary of living so long . . . far too long. My young master's presence lends spice to the world we're glutted on."
- On Sebastian's grave, his epitaph included the following inscriptions: 'To The Memory of Sebastian Michaelis. Died March 1889. May ye be in heaven an hour before the devil knows you're dead."
- In the Victorian era, butlers were called by their last name. So Sebastian should technically be called Michaelis by Ciel and Mr. Michaelis by the other servants.
- When Sebastian was summoned in the manga, he appeared in his true demon form; in the anime, he appeared as a crow or raven accompanied by a rain of feathers.
- Sebastian got his last name from the Japanese word mikairi meaning "repayment."
- Sebastian's name is similar to Father Sebastien Michaelis, who wrote a classification of demons in Hell.
- The word Sebastian uses is “gyoi” (御意) = “as you wish” / “very well”. The kanji literally mean “your (honorable) will/pleasure”. (Credit goes to Grimm-san from Words Across the Ocean for this trivia).
|Ciel Phantomhive · Vincent Phantomhive · Rachel Phantomhive · Sebastian Michaelis · Tanaka · Baldroy · Mey-Rin · Finnian · Pluto · Snake|
|Baron Kelvin · Joker · Beast · Dagger · Wendy · Peter · Jumbo · Snake · Doll · Doctor · Suit · Smile · Black|
|Sebastian Michaelis · Claude Faustus · Hannah Anafeloz · Cantebury · Thompson · Timber|
|The principal • Johan Agares • Mr. Michaelis|
|Edgar Redmond • Gregory Violet • Herman Greenhill • Lawrence Bluer|
|Cheslock • Clayton • Edward Midford • Joanne Harcourt • Maurice Cole • Derrick Arden|
|Ciel Phantomhive • Derrick Arden • McMillan • Prince Soma|