Karen Minazuki, who transforms into Cure Aqua, is a character whose journey spans from her middle school days to her adult life in the series Power of Hope: Precure Full Bloom. As a student at L'École des Cinq Lumières, she held the position of student council president and was widely admired by her peers for her calm, mature, and highly intelligent demeanor. Coming from an affluent family, her parents were touring musicians who were frequently absent due to their careers, leading to her being primarily raised by her butler, Jii-ya. This upbringing, while providing material comfort, instilled in her a deep sense of loneliness that she often masked behind a stoic and self-reliant exterior, choosing not to burden others with her feelings. She was initially skeptical of the Pretty Cure concept and, despite an opportunity to transform, her first attempt failed because her motivation was driven by a sense of duty rather than a genuine heartfelt desire to protect others. It was only after witnessing her friends in danger and acknowledging her true wish to protect them that a blue butterfly, a symbol of her resolve, returned to grant her the power to become Cure Aqua, the Pretty Cure of Intelligence.

Her core personality is defined by a contrast between her outward composure and internal vulnerabilities. While she is known for her grace, strategic mind, and reliability, she could sometimes come across as emotionally reserved or, under prolonged stress, make uncharacteristically harsh remarks. A significant part of her character arc involves learning to open her heart to others and express her emotions more freely. Her friendship with the persistent and earnest Nozomi Yumehara was pivotal in this development, as Nozomi’s unwavering belief in her helped Karen overcome her loner mindset and accept the power of teamwork. She shares a particularly deep bond with Komachi Akimoto, her best friend and classmate, who has been a source of emotional support since a challenging middle school project. Her relationship with Rin Natsuki is notably different, characterized by a rivalry that reflects their opposing elemental motifs of water and fire, as well as passion versus intelligence; despite their frequent arguments, this dynamic grew into a mutual respect and a stronger friendship through shared battles.

In Power of Hope: Precure Full Bloom, Karen is depicted as having achieved her dream of becoming a doctor, a career path inspired by her bond with Milk (Kurumi Mimino), a younger character who admired her grace. Her professional life as a physician, however, comes with its own challenges, such as learning to treat a distrustful patient with greater empathy, showcasing her continued growth in integrating her intelligence with emotional warmth. The sequel finds her balancing the demanding responsibilities of a medical career with her revived duties as a Pretty Cure, as former teammates reunite to face a new crisis that drains their life energy when they transform. This chapter of her life highlights her seasoned leadership and the maturity she has gained, transitioning from a solitary student president to a compassionate protector who uses her skills to heal and safeguard lives.

As Cure Aqua, her abilities are intrinsically linked to the element of water. She wields a variety of precision-focused attacks, demonstrating her role as the team's tactical leader who devises effective strategies during combat. Her signature techniques include the powerful torrential attack Precure Aqua Stream, its enhanced version Precure Aqua Tornado, and later, the projectile attack Precure Sapphire Arrow. Her transformed appearance is characterized by her long blue hair tied into a ponytail with a butterfly-shaped bow and an aquatic-themed outfit with scalloped layers, reflecting her graceful and intelligent nature. Her journey from a lonely, duty-bound student to a confident doctor and reliable Cure is marked by her learning to value friendship, embrace her emotions, and ultimately choose a life dedicated to the service and protection of others.