Amaterasu is a central character in the Onigiri series, appearing as the goddess of the sun who once vanquished the monsters known as Kamikui. Several years before the events of the story, she mysteriously disappeared and began to consistently lose her powers, a process that caused her body to de-age into the form of a young child. After being rescued from captivity in Kyoto, she willingly joins the main group of eight brave warriors to find a way to regain her original, more mature body. The anime adaptation portrays her as having lost much of her power following the destruction of an old seal, which is why she now exists in the form of a little girl.

In her original, true form, Amaterasu was a great goddess of immense beauty, described poetically with the notion that where she stands, chrysanthemums bloom; where she sits, peony flowers grow; and where she walks, a garden springs forth. In her shrunken, childlike state, her personality is cheerful and she makes the best of her weakened condition, often acting like a young child. She refers to the other members of her party as if they were her older brothers or sisters, with the only exception being her brother, Susanoo. Although she typically carries herself with a youthful demeanor, she sometimes sulks about her childish body because in her original form she was well-endowed. Despite her playful nature, her true age grants her wisdom beyond her apparent years, and she takes her role as a goddess seriously, offering advice about the realm of the gods when it is necessary.

Her primary motivation is to regain her lost power and original body, a goal that drives her participation in the group's adventures. In the context of the story, she becomes the eighth and final member of the party, joining them after being freed from captivity. Her key relationships within the group are defined by the familial affection she shows them, treating them as older siblings. Her most significant specific relationship is with her brother, Susanoo, whom she addresses differently than the rest of the party. Although she has lost most of her former power, she still retains some abilities in her weakened state. Her role is primarily that of a support character, as she professes herself in supporting the player with the world around her. She possesses the ability to strengthen the bonds between people, a power known as Nigimitama, which allows her to enhance the abilities of her companions. She can also bestow feelings of happiness and joy upon others, a power called Sakimitama, which manifests as a gift that grants others stat points to use. Furthermore, as the goddess of the sun, she has vast connections with famous names, enabling her to grant titles to the player that provide certain stat bonuses in exchange for fulfilling specific requirements, an ability referred to as Blossoming Talent. Her growth is tied to her affection level with the player; as this level rises, her supportive abilities become progressively more effective, enhancing her companions' powers, granting more stat points, and unlocking higher and more well-known titles.