Bound by a Faustian contract to serve Ciel Phantomhive, the young Earl of Phantomhive, the demon Sebastian Michaelis originated this pact when summoned by Ciel during a sacrificial ritual conducted by a cult imprisoning and torturing the boy. The demon agreed to act as Ciel's butler and protector in exchange for eventually consuming his soul, adopting the name "Sebastian Michaelis" from the Phantomhive family's deceased pet dog. This contract demands absolute obedience to Ciel's commands, forbids lying to him, and requires protection until Ciel achieves his revenge. A visible pentagram mark on Ciel's right eye signifies the pact, mirrored by a corresponding mark on Sebastian's left hand. Sebastian existed as a demon for centuries before serving Ciel, interacting with humans across historical periods including ancient Egyptian rituals and European witch trials. This long existence informs his view of human lives as fleeting and fuels his culinary interest in human souls, which he judges as varying in quality. His true, amorphous, monstrous form manifests as a shifting mass of darkness featuring multiple eyes, mouths, and appendages, capable of assuming shapes like serpents, wolves, or crows. He finds this form unsettling to humans and typically maintains a human guise. As butler, Sebastian presents himself as impeccably formal, efficient, and multi-skilled, managing all Phantomhive estate duties with superhuman precision. He oversees staff, finances, security, and Ciel's responsibilities as the "Queen's Watchdog," investigating criminal underworld activities on Queen Victoria's orders. He recruits and trains the estate servants—Mey-Rin, Finnian, and Baldroy—each possessing hidden combat abilities aiding Ciel's protection. Despite his composure, he displays a fondness for cats, particularly black ones, and secretly keeps them. Fluent in numerous languages including German, East Franconian dialect, French, and Latin, he is also proficient in cultural practices like the Viennese waltz. His personality blends sardonic humor with detached cruelty, often mocking human frailties or toying with enemies while fulfilling the contract. During the Emerald Witch Arc, Sebastian accompanies Ciel to Germany's Werewolves' Forest to investigate mysterious deaths under the Queen's orders. Victims exhibited grotesque physical deformities and madness, attributed locally to a witch's curse linked to the forest. Sebastian acts as Ciel's translator due to Ciel's limited German, facilitating interactions with hostile villagers. Initially dismissive of the curse, both succumb after encountering a spectral wolf entity, experiencing symptoms including nosebleeds, facial swelling, and psychological trauma, marking a rare instance where supernatural forces overcome Sebastian's demonic resilience. Sieglinde Sullivan, a self-proclaimed witch and descendant of the Emerald Witch, performs a cleansing ritual to alleviate their condition. During Ciel's recovery, Sebastian temporarily serves Sullivan at her request, showcasing adaptability by preparing elaborate meals and instructing her in modern etiquette. This arc reveals Sebastian's contractual limitations; his inability to fully protect Ciel underscores that his powers are constrained by the pact's terms and specific supernatural threats. Sebastian's loyalty remains strictly contractual, not personal. He occasionally manipulates or tests Ciel during vulnerability to provoke emotional reactions or assess resolve. This dynamic complicates with revelations that Ciel is actually the younger twin of the original Ciel Phantomhive, whose identity he assumed after the cult sacrificed his brother. Sebastian acknowledges this deception without altering his contractual obligations, focusing solely on the summoning pact terms. His ultimate goal remains consuming Ciel's soul, which he anticipates as a "delicious" reward once the contract concludes.