Ai Amatsu is one of two protagonist twin sisters and the older fraternal twin, distinguished by her longer brown hair typically worn in a long ponytail that reaches her hips or beyond. She has striking purple eyes and stands 160 centimeters tall, born on June 10th. Ai and her younger sister Mai are descendants of a mortal fisherman and a Tennyo, a celestial angel from Buddhist tradition, a sacred lineage that designates them as virgin priestesses and guardians. Orphaned at a young age after the death of her ill mother and short-lived father, Ai was raised by her adoptive grandmother, Amatsu Genshu, who trained the twins from childhood in spiritual traditions, martial arts, and the ancient Tenjin dances. Their primary mission is to protect Onimaru, a young half-demon and distant relative whose choices could either plunge the world into debauchery or preserve its current state. As a virgin priestess, maintaining physical and spiritual purity is vital to her role against demonic forces that use sexual perversion as a weapon. Ai is strong-willed and competitive, with a fierce sense of responsibility and a refusal to lose, especially to men—she is an avowed man-hater who will ignore any man who speaks to her. Despite her tomboyish demeanor, her manner of speech remains feminine, polite, and proper. She is deeply caring and gentle toward her sister Mai, and more devoted to her obligations than her sibling. Ai wields a bow as her primary weapon, a renowned master of archery who has participated in the Tenjin Offering Archery Competition. After being told of the Amatsu family mission, she is bestowed with a celestial robe and a branch of a plum tree; using her spiritual powers, she shrinks the robe and wears it as a ribbon to tie her hair. Later, she masters the Heavenly Robe Dance, allowing her to inherit the full power of the robe legend, and in that transformed state she fires arrows to vanquish evil demons.