Ai Amatsu, the elder twin distinguished by her longer brown hair often in a ponytail and purple eyes, shares a celestial heritage with her sister Mai. They descend from a Tennyo angel born to a fisherman, inheriting sacred duties as virgin priestesses and legendary warrior guardians. Their primary mission is protecting Onimaru, a half-demon whose choices threaten to save the world or unleash demonic debauchery. Guided by their grandmother, Amatsu Genjuu, and aided by the guardian Dekonobu, they operate against demonic forces seeking to corrupt Onimaru into a demon king by exploiting his ancestral grudge.

Ai exhibits a strong sense of obligation, often showing greater devotion to their duties than Mai. She wields her bow in combat against demons intent on capturing Onimaru, spreading sexual perversion, and claiming victims to plunge the world into chaos. The twins constantly resist attempts to compromise their chastity, a vulnerability their enemies exploit. Ai's role demands vigilance against supernatural threats and the moral complexities surrounding Onimaru's potential fall. Their story weaves together ancestral legacies, supernatural battles, and the preservation of sacred duties amid relentless opposition.