Karen Minazuki is Cure Aqua, the Pretty Cure of Intelligence. As a third-year student council president at L'École des Cinq Lumières, she memorizes every student's name and face. Her calm, stoic exterior often conceals loneliness stemming from her parents' frequent absence, which once led her to shoulder burdens alone. This emotional guardedness surfaces in harsh remarks during stress, like criticizing Komachi Akimoto's indecisiveness. Komachi remains central to her life after inspiring her during a difficult first-year project, preventing her from quitting and forging an inseparable bond. She shares a protective relationship with the fairy Milk, who admires her grace, and respects her caretaker Jii-ya, heeding his counsel. Initially clashing with Natsuki Rin (Cure Rouge) due to opposing personalities, they gradually developed mutual friendship.

Cure Aqua commands water-based powers, reflecting her name's meaning: "Minazuki" references June (a rainy month) and "water" (水), while "Aqua" is Latin for water. Her transformed state features bright blue eyes and waist-length blue hair in a ponytail secured by a butterfly-shaped bow. Her costume consists of a cream mini-dress, blue shorts, boots with butterfly motifs, and water-pistol-like weapons. Enhanced forms like Super Cure Aqua and Rainbow Cure Aqua introduce scalloped layers, wings, and intensified blue hues.

In *Precure All-Stars DX3*, Cure Aqua allies with blue-themed Cures (Cure White, Egret, Mint, Berry, Marine) in an oceanic dimension. She strategizes to destroy a witch's crystal for escape. Later, she comforts Milk facing separation from humans and joins the unified Rainbow Pretty Cure attack to defeat Black Hole.

*Pretty Cure 5☆Reborn* introduces her non-biological younger sister, Minazuki Kelly (Cure Sapphire). Karen immediately embraces Kelly, supporting her in battles and encouraging her during a Kowaina attack, demonstrating strong familial loyalty. A spin-off film reveals her destiny as the "chosen champion" of the Crystal Waters to confront Dark Aqua. This journey forces her to confront inner doubts about her past and powers, ultimately accepting her role with her team's support and learning to trust others.

Personality analyses identify her as ISTP/INFJ with Enneagram Type 1w2, noting strategic thinking, perfectionism, and empathy. These align with her disciplined leadership, battlefield adaptability, and introspection. Her development consistently shows her overcoming isolation through friendships, balancing duty with emotional openness, and affirming her identity as a guardian and sister figure.