Chloe Aubert is a central figure in the narrative, initially appearing as one of several children who were incompletely summoned to the world from another. Her background is marked by this flawed summoning, which leaves her with a fatal condition: her young, fragile body contains a dangerously unstable and immense amount of magic essence, threatening to consume her from within. She resides at the Freedom Academy in the Kingdom of Ingracia alongside other children in a similar predicament. Her fate takes a decisive turn upon meeting Rimuru Tempest. Recognizing her plight, Rimuru takes her to the Spirit Sanctuary, where her soul is fused with a powerful entity named Chronoa, saving her life. Following this, she is given the original anti-magic mask that belonged to Shizue Izawa and is taken under Rimuru's protection, moving to the nation of Tempest to live and study at his new school.

In her everyday life, Chloe is a quiet, introverted, and gentle ten-year-old girl who is often seen with a book in hand. She appears reserved and stoic, though this demeanor masks a profound emotional depth and an incredibly strong will. She is deeply loyal to her friends and cherishes her peaceful life. However, her personality is notably different around Rimuru, whom she calls teacher or professor. With him, she becomes more playful, affectionate, and boldly forward, sometimes showing a competitive side with her friend Alice for his attention. Her feelings for him mature into a clear and openly expressed romantic love, which she has demonstrated on multiple occasions, including stealing kisses.

The depth of her motivation becomes clear as her true nature is revealed. Chloe is the legendary Masked Hero known as Chronoa, a time-traveling warrior who has lived through countless tragic futures. Her primary drive is the protection of her loved ones, especially Rimuru, whom she has witnessed dying in many past timelines. She is trapped in a tragic time loop: every time her close friend Hinata Sakaguchi is killed, Chloe’s unique ability activates, sending her and Hinata’s soul two thousand years into the past. In that past, she uses the name Chronoa and, over millennia, forges alliances, grows immensely powerful, and becomes the hero who ultimately seals the Storm Dragon Veldora in the cave where Rimuru would later be reincarnated. At the end of each loop, she is sealed away by her ally Luminous Valentine, only to be reawakened in the future, repeating the cycle in a desperate attempt to change the outcome for everyone she holds dear.

Her role in the story is therefore multifaceted. She is first a child under Rimuru’s care, but she ultimately reveals herself as one of the most powerful and crucial protectors of Tempest. Her actions in the past are directly responsible for the world's present state, including the sealing of Veldora which set the entire plot in motion. She is a trump card against world-threatening calamities and a key fighter in the battles against the otherworldly forces that seek to destroy Rimuru’s nation.

Her key relationships are deeply entangled with her temporal journey. Rimuru Tempest is the most important person to her, her teacher, and the one she loves; her entire goal across countless loops is to create a future where he survives. Hinata Sakaguchi is another pivotal figure; her death triggers the time loops, and her soul merges with Chloe’s during these journeys, influencing her abilities and giving her the name Chronoa. Luminous Valentine becomes a close friend and trusted ally over the many loops, helping Chloe and eventually sealing her to preserve her for the future. Leon Cromwell is revealed to be her childhood friend from her original world. They were separated when she was abruptly summoned into the future, and his obsessive quest to perform targeted summonings across centuries is driven by his desire to find her again. Her connection to Shizue Izawa is symbolic, carried through the infinite paradox of the anti-magic mask, which passes from Shizue to Rimuru, to Chloe, and then back to Shizue through time.

Chloe’s development is a tragic arc of accumulated experience. She evolves from a fragile, doomed child into the strongest hero in history. This growth is not linear but cyclical, as each time loop adds layers of memory, trauma, and power. After being rescued by Rimuru, she eventually integrates her Chronoa personality with her child self, gaining full control over her immense power and breaking free from the endless, predetermined tragedy of her loops. This allows her to finally live as both a student and a guardian, choosing to stand beside Rimuru as an equal rather than as a dependent.

Her notable abilities are staggering, making her one of the most powerful beings in the world. Her primary power is time manipulation. Initially, this manifests as the unique skill Time Travel, which involuntarily sends her to the past upon a specific trigger. With Rimuru's influence, this evolves into the ultimate skill Space-Time King Yog-Sothoth, granting her complete mastery over time and space, including the ability to stop time entirely. She later acquires the ultimate skill Hope King Sariel, governing life and death, and even seizes partial authority over Justice King Michael, an ability of the highest order. She has access to other potent skills as well, including the Usurper ability to copy others' powers, the Infinite Prison to create an inescapable seal, and Melt Slash, a sword technique that moves faster than light. With the integration of Chronoa and her millennia of battle experience, Chloe is a master swordswoman whose power is directly compared to the strongest demon lords, making her an irreplaceable asset in the final battles for the fate of the world.