Ciel Phantomhive is the young Earl of the Phantomhive family and the protagonist of Black Butler, known for his refined appearance, sharp intelligence, and composed demeanor despite everything he has endured. He is a small, slender boy with dark blue hair, striking blue eyes, and a distinctive eyepatch covering one eye, usually dressed in elegant Victorian aristocratic clothing that reflects his noble status. Ciel is highly intelligent, observant, and calculating, often able to analyze situations and manipulate circumstances to his advantage. Although he can appear cold, arrogant, or demanding, his harsh personality is largely shaped by the traumatic experiences of his past and his determination to achieve his goals. He takes his duties as the head of the Phantomhive household and the Queen's Watchdog seriously, investigating unusual incidents and protecting the interests of the Crown. Ciel is also proud and dislikes showing vulnerability, preferring to maintain control even when he is frightened or emotionally overwhelmed. Despite his young age, he possesses remarkable business skills and manages the Phantomhive family's company while navigating dangerous supernatural and political situations. His relationship with his mysterious demon butler, Sebastian, is built upon a contract in which Sebastian serves him faithfully until Ciel's ultimate goal is accomplished, making their partnership both powerful and complicated.

Sebastian Michaelis is the elegant and mysterious demon butler who serves Ciel Phantomhive in Black Butler, distinguished by his impeccable manners, extraordinary abilities, and seemingly effortless perfection. Tall, slender, and strikingly handsome, Sebastian has black hair, crimson-red eyes, and usually wears a sophisticated black butler's uniform complete with gloves, embodying the image of a flawless Victorian gentleman. He is exceptionally intelligent, calm, observant, and capable of handling almost any situation with remarkable ease, whether he is preparing an elaborate meal, managing the Phantomhive household, fighting supernatural enemies, or protecting Ciel from danger. Sebastian rarely loses his composure and often maintains a polite smile even when dealing with threatening or chaotic circumstances. Beneath his courteous butler persona, however, he is a powerful demon who views humans with a mixture of amusement and curiosity, and his loyalty to Ciel ultimately exists because of the contract between them rather than ordinary human affection. He takes great pride in his abilities as a butler and frequently expresses the idea that he must fulfill his master's orders perfectly, no matter how difficult they may be. Sebastian can be playful and teasing, particularly when Ciel becomes frustrated, but he remains attentive to his master's commands and protects him whenever necessary. His combination of elegance, supernatural power, dry humor, and unwavering professionalism makes him one of the most memorable characters in the series.