Clarisse de Cagliostro is the young princess and rightful ruler of the European Grand Duchy of Cagliostro. She is a very beautiful young woman with short auburn hair, blue eyes, and fair skin. Orphaned at a young age, her parents, the Grand Duke and Duchess, died in a fire that also destroyed their home. Following their death, she was sent to a convent for her upbringing before returning to the duchy when she came of age.

In terms of personality, Clarisse is fundamentally kind, gentle, and sweet, but her sheltered upbringing has left her somewhat naive about the wider world. Despite this initial innocence, she displays a surprising amount of inner strength and courage, particularly when defending what she holds dear. While she initially appears as a passive victim who accepts her fate, her character demonstrates a clear evolution. In her darkest moments, she believes she will never be able to escape the Count's control, yet she consistently finds the resolve to act. She shows great bravery by standing up to the Count, calling him a murderer, and physically pushing him away. She is also willing to sacrifice her own life to protect Lupin and Fujiko from gunfire.

Clarisse's primary motivation within the story is to escape her forced marriage to Count Lazare de Cagliostro, a cruel and greedy distant relation who has assumed guardianship over her. The Count seeks to marry her solely to gain access to the legendary hidden treasure of the Cagliostro family, to which her signet ring is a key. Her role in the narrative is largely that of a damsel in distress whom Lupin seeks to rescue, but she is far from a passive object. Her plight drives the main conflict, and her actions are crucial to the film's climax, such as when she shoves the Count from the clock tower.

The most significant relationship in Clarisse's life is with Arsène Lupin III. She first encountered him as a young girl when he was a wounded young thief who had stumbled into her family's gardens. Instead of alerting anyone, she secretly brought him a glass of water, an act of kindness that helped him recover. Ten years later, when Lupin rescues her from a car crash, he only fully remembers their shared past when he sees her signet ring. This memory transforms his goal from simply finding a treasure to personally saving her from the Count's clutches. Throughout the adventure, Clarisse falls deeply in love with Lupin, who is genuinely moved by her. At the conclusion of the story, she asks to remain with him, even declaring she is willing to become a thief, but Lupin gently refuses, not wanting to drag her into his dangerous world, though he promises to help her again should she ever need it. This promise is seemingly honored in later media, where Clarisse allows Lupin to take refuge in Cagliostro's catacombs.

Clarisse's development throughout the film is marked by a transition from a meek, resigned captive to a young woman of decisive action. She escapes from a mansion protected by lasers, participates in a high-speed car chase, saves Lupin's life on multiple occasions by pushing him from the path of bullets, and ultimately confronts her captor directly. While she does not possess supernatural or martial abilities like other characters in the series, her notable ability lies in her emotional courage and the strength she draws from her compassion. She is also admired by the citizens of Cagliostro, who hold her in great affection. In addition to her rescue, she is notable for leaving a lasting impression on Lupin's companions; Jigen is so moved that he wears her discarded wedding crown on his fedora for the remainder of the film.