Aoi Kannazuki, alias Blue Angel, attends St. Cherine Academy as a first-year camellia group student. Born October 23, she stands 157 cm tall, weighs 43 kg, and has body measurements of 91-58-88 cm (G-cup). Her image color is blue, reflected in short blue hair with an ahoge and violet eyes, typically accessorized with a white headband. She wears glasses during classes but removes them elsewhere.

Hailing from the affluent Kannazuki family, her grandmother serves as St. Cherine's principal. After childhood friend Haruka Minazuki lost her parents, Aoi's family took Haruka in, and they now live together. Aoi maintains a ladylike, refined facade but occasionally surprises others with airheaded behavior. Academically exceptional with top national test scores, she excels in archery yet struggles in most sports, particularly endurance activities like marathons.

By night, she transforms into Blue Angel, a Phantom Thief Angel defending the Seven Amulets against the evil Black Fund. Her blue-based battle outfit features feather-like shoulder designs and navy frilled thigh-highs. She wields a magical bow generating infinite arrows for long-range combat, employing signature techniques "Angel Arrow" and "Angel Thousand Arrow"—the latter firing multiple projectiles simultaneously.

As Blue Angel, she anchors the team as Haruka's (Red Angel) calm, logical counterpart during missions, though she occasionally teases Haruka with mischievous or puzzling remarks. Her core personality remains fiercely strong-willed. Through battles against antagonists like Black Trader and the Violet sisters—Tesla and Nine, who later defect after uncovering Black Trader's deceit—Aoi deepens her partnership with Haruka and reconciles with former enemies turned allies.

Her lineage connects to previous Angels; her grandmother once held the Blue Angel mantle. In later events, Aoi and Haruka vanish, prompting their cousin Kurumi Hazuki (White Angel) to recruit trainees Meguru Amatsuki and Sumire Kisaragi to inherit the Twin Angel legacy.