Ami Gidou transforms into Blue Princess following recruitment by the Moon Cat Gi-chan. She possesses fair skin, sharp teal eyes, and pastel blue shoulder-length hair worn beneath a white headband, with long forelocks framing her face. In civilian life, she attends school and works at her adoptive parents' Chinese restaurant, dressed in a dark blue and yellow gown with an apron, sheer tights, and black heels, often styling her hair in buns secured by pale pink covers. Supporting her family's struggling business reveals her hardworking and responsible nature, though she experiences loneliness and exhibits tsundere tendencies in specific scenarios.

As Blue Princess, her hair extends to waist length with curled sections. Her costume features a gold tiara with three white diamonds and wings, blue heart gem earrings, and a dark blue choker. The outfit consists of a white frilly dress with a dark blue chest ribbon bordered in white and centered by a blue gem. A pale blue tutu overlays a frilly white petticoat, topped by a white flower-shaped peplum. She wears a pale blue and white belt displaying a diamond motif, suspending a pink and white purse on a striped strap. Additional elements include a pointed light blue ribbon on the back, white wrist accessories with dark blue bands and pale blue fabric accents, white thigh-high socks adorned with blue diamonds, and white boots detailed in pale blue with pointed heels. The peony mark symbolizing her connection to the Heart Princesses rests on her back.

Gi-chan first approached her on a bridge to propose becoming a Heart Princess, an offer she initially rejected. During a Zaiju attack at a marketplace—where Haruka transformed into Pink Princess—Gi-chan reappeared in human form, invoking memories of Ami's adoptive parents. Motivated by loyalty to her family, Ami accepted the role. The phrase "Condensed Telepathic Transfer!" activated her transformation, imprinting the peony mark and granting Blue Princess powers. She embodies the virtue of "Gi" (justice), reflected in her determined personality and commitment to righteous battles. In combat, she wields a Heart Wand, replacing an initially planned umbrella weapon.

Her relationships include a complex dynamic with Rokkaku, an Earth Wolf antagonist who develops a crush on her despite their opposing roles. She remains the only Heart Princess documented to smile during her transformation incantation.