Karen Minazuki, known in her transformed state as Cure Aqua, is a central character who appears in the Precure All Stars DX film series as a member of the Yes! Pretty Cure 5 team. Her background establishes her as a third-year student and the respected student council president at L'École des Cinq Lumières, an elite academy. She comes from an extraordinarily wealthy family; her parents are world-renowned musicians, a pianist father and violinist mother, whose constant international tours leave her living alone in a large mansion. Consequently, she was primarily raised by her devoted butler, Jii-ya or Sakamoto, a situation that instilled in her a profound sense of loneliness despite her material privilege. Academically gifted and athletic, she excels in horseback riding, tennis, and water skiing, yet ironically struggles with mundane domestic tasks like cooking, often approaching recipes with an overly scientific and numerical focus that leads to unusual results.

Personality-wise, Karen presents a calm, stoic, and highly intelligent demeanor, which makes her an object of admiration among the student body. However, this composed exterior serves as a mask for her underlying vulnerability and isolation. Initially, she firmly believes that she must shoulder all burdens alone, refusing to depend on others due to the emotional distance created by her absent parents. This internal pressure sometimes causes her to suppress her feelings, and when stressed or angered, she can become unexpectedly harsh, such as when she sharply criticized her best friend, Komachi Akimoto, for indecisiveness. This emotional guardedness was the primary obstacle in her journey to becoming a Pretty Cure. The first time a blue butterfly, the symbol of her power, appeared to her, she was too terrified and doubtful to accept it, causing the transformation to fail. Her motivations shift from reluctant acceptance to fierce dedication after witnessing her friends fight to protect others. Encouraged by the persistent optimism of her teammate Nozomi Yumehara, she overcomes her self-doubt and vows to fight alongside them, unlocking her full potential as Cure Aqua, the Pretty Cure of Intelligence.

Within the narrative of the Precure All Stars films, which bring together heroes from different seasons, Karen role is that of a tactical leader and a reliable strategist. Her defining trait is her sharp, analytical mind, which she uses to assess enemy weaknesses and coordinate plans in high-stakes, cross-over battles. For instance, in confrontations against massive foes like Fusion or within trapped dimensions, she is often the one calculating the most efficient escape route or attack pattern, such as formulating a strategy to destroy a witch's crystal in an oceanic dimension. Her key relationships significantly shape her development. Her bond with Komachi Akimoto (Cure Mint) is the most vital; Komachi inspired her during a difficult first-year school project, preventing Karen from giving up, and they share an inseparable, supportive friendship. She also shares a unique, protective dynamic with the fairy Milk (Milky Rose), who admires Karen grace and maturity, and this nurturing role partly inspires her later desire to become a doctor. Initially, she clashes with the more hot-headed Rin Natsuki (Cure Rouge), but their contrasting personalities eventually forge a relationship of mutual respect and camaraderie.

Throughout her appearances, Karen development is marked by a transition from emotional isolation to embracing vulnerability. She learns to trust her teammates, shed her rigid perfectionism, and express joy openly, even occasionally cracking very bad jokes, which her butler notes as a sign of genuine growth. In the All Stars continuity, she stands alongside other blue-themed Cures, showcasing a unified front and contributing her intellectual prowess to the group. As Cure Aqua, her notable abilities are entirely water-based, reflecting the meaning of her name, where Minazuki refers to the rainy month of June. Her signature attacks include Aqua Stream, where she releases a powerful jet of water from the butterfly emblem on her hand, and its upgraded form, Aqua Tornado, which she performs using the Aqua Ribbon to create a vortex or blade of compressed water energy. In the sequel series, she gains the ability Sapphire Arrow, summoning a bow made of water to fire multiple projectile arrows, establishing her as an archer archetype within the team. Her transformed state features waist-length blue hair tied with a butterfly-shaped bow and a cream-and-blue costume, with later power-ups like Rainbow Cure Aqua introducing angelic wings and layered details.