Marie is portrayed as a mature and serious young girl, particularly when it comes to her work as a clockmaker. Considered a prodigy, she is often described as one of the most gifted engineers in history, and is known for her uncompromising focus going so far as to threaten anyone who interrupts her while working. Despite this immense talent, she is cooperative and pragmatic, choosing to collaborate with fellow members of the Meister Guild and even camping alongside them in difficult conditions rather than enjoying the privileges of her social status. She also demonstrates humility by discarding her prestigious Meister title in order to stage her own death. Like Naoto Miura, she takes pride in her craft and is unafraid to argue with those who belittle her work.

Though skeptical of human religions, Marie acknowledges the possibility of higher powers, admitting that she has received revelations in moments of crisis, such as before the Kyoto Purge. She also exhibits a strong sense of morality, shown when she refused to abandon Kyoto and instead vowed to repair its Core Tower to save millions of lives. Unlike those she criticized for walking away, Marie accepted responsibility, choosing to attempt the impossible rather than resign the city to destruction.

Despite her skill and family pedigree, Marie is still a child and often requires the support of Halter and her allies in Second Upsilon. She is outspoken and brash, yet considers herself more lenient than her elder sister, noting that while her sister might execute people without hesitation, she herself could not. Her immaturity is also evident in moments of emotional distress, such as when she vomited from stress after believing Naoto had died. Halter frequently reminds her to allow herself the freedom to enjoy life as a child.

Marie’s personal habits further reflect her youthful side. She has a preference for junk food and candy especially chocolate because of the energy her work demands, despite having access to far finer cuisine. She also harbors a fondness for absinthe from Paris, hinting at her longing for experiences beyond her immediate duties.

Marie is a young French girl with long blonde hair, typically tied into two bunches with red ribbons. She has emerald-green eyes and thin pink lips, giving her a refined yet youthful appearance.

Her usual attire consists of a deep-blue collared shirt paired with a pink tie, short denim shorts, and a beige summer overcoat decorated with blue patterns and linings. This combination reflects both her practicality as a clockmaker and her distinctive personal style.

Marie is recognized as a first-class clockmaker and was the youngest individual to ever attain the prestigious title of Meister. As a member of the distinguished Breguet family, she underwent rigorous training from an early age, mastering the strengths and weaknesses of their designs. By the age of thirteen she had already enrolled in advanced studies, graduating with a doctorate from several renowned universities before turning seventeen. Her extensive education, combined with practical experience from numerous engineering projects, allows her to perceive minute changes in the planet’s systems, such as gravitational fluctuations of less than 0.1 in magnitude. However, even with her skills, she was initially unable to repair RyuZU.

Marie’s abilities extend beyond technical genius; she is capable of building upon existing knowledge to rediscover and expand on the breakthroughs achieved by Y a century earlier. This talent places her on par with Naoto Miura, her fellow prodigy in Second Upsilon. While Naoto intuitively hears the “answers” and works backward toward the solution, Marie constructs solutions step by step, applying theory and practice to reach the same results.

In addition to her mechanical expertise, Marie is also a skilled gymnast and martial artist, giving her the agility and combat proficiency to defend herself when necessary.

Breguet Family
Marie holds her family in high regard, demonstrating deep respect for their expertise and resources. She knew that her family would possess the necessary parts to repair AnchoR, reflecting her confidence in their capabilities. She also frequently compares herself to her elder sister, noting that while she is relatively forgiving, her sister is far harsher and would punish anyone who wronged her without hesitation.

Vainney Halter
Halter serves as Marie’s personal bodyguard and remains by her side throughout much of the series. While their relationship begins as a professional arrangement, it develops into a close bond. Halter not only protects her but also helps temper her sharp tongue and tendency to anger, often preventing her from causing unnecessary conflicts. He affectionately refers to her as “Princess” (Hime-san).

Hannes
Marie regards Hannes as an essential member of the repair team and places trust in his technical abilities. In return, Hannes respects her greatly, addressing her as “sensei” in acknowledgment of her talent.

Conrad
Marie values Conrad as both an advisor and skilled repairman, frequently relying on his insights. Conrad, in turn, sees Marie as a brilliant young prodigy who requires mentorship and guidance to fully realize her potential.

Massimo
Marie views Massimo as an indispensable part of the repair team, relying on his estimations without hesitation. Massimo respects her abilities and never displays resentment toward her youth or position, instead recognizing her as a capable leader.

Marie’s full name, Marie Bell Breguet (マリー・ベル・ブレゲ), reflects her European origins and connection to the historically significant Breguet family. The surname Breguet is a direct reference to the real-world Swiss horologist Abraham-Louis Breguet, a pioneering watchmaker whose innovations in clockwork and timepieces influenced modern horology. Her given name Marie Bell emphasizes her noble background, with “Bell” likely serving as an allusion to both refinement and resonance, echoing the mechanical theme of sound and precision associated with clocks.

Her later alias, Maribel Halter, incorporates the surname of her bodyguard, Vainney Halter, symbolizing the deep bond between them and her shift in identity following the events of the series.