Hinata Taiyo, the deceased mother of protagonist Akari Taiyo, was a professional fortune teller wielding a family-inherited tarot deck. As a member of the secret organization Sefiro Fiore, she fought Daemonia—monsters born from humans consumed by despair—using the power of her Elemental Tarot card, "The Sun". This duty required eliminating the possessed human hosts.

Determined to give Akari a normal life, Hinata deliberately concealed her Sefiro Fiore involvement and never trained her daughter in using the Elemental Tarot. This choice directly resulted in Akari's unpreparedness when she eventually inherited the "Sun" card's latent power, awakened through Hinata's passed-down deck.

The light novel prequel depicts Hinata's active service alongside comrades like Amelie Lamour, wielder of "The Lovers". Her story explores collaboration with Hajime Takatori, a Sefiro Fiore Daemonia researcher implied to be Akari's father. This connection established Hinata's relationship with a Daemonia, making Akari a half-human, half-Daemonia hybrid—a heritage crucial to Akari's later ability to hear Daemonia thoughts.

Hinata's physical legacy includes a distinctive hereditary hairstyle featuring a crescent-shaped hair ornament, inherited by Akari. Her background as a fortune teller and her commitment to protecting balance, despite the moral weight of killing possessed hosts, define her character. Her choices and undisclosed past directly shape Akari's journey and the series' central conflicts.

Though Hinata's death precedes the main series events, her absence and unresolved history persistently influence the narrative, particularly Akari's struggles with her lineage and duties. Her legacy unfolds through Akari's interactions with the inherited tarot deck and revelations about their family's connection to the Daemonia threat.