Hanyū serves as Rika Furude's ancestor and the true form of Hinamizawa's revered goddess, Oyashiro-sama. Her appearance is that of a young girl characterized by purple eyes and long light purple hair, always featuring a pair of dark purple horns—one visibly cracked. She typically wears traditional shrine maiden attire with a red bow and light red sleeves, though she adopts human forms like school or casual clothing as needed. Her look remains constant across time, including an adult depiction in the Kotohogushi-hen backstory.

Centuries ago, Hanyū arrived with her clan at Onigafuchi (later Hinamizawa) seeking refuge. Discrimination arose due to her horns, but she married Furude Riku, bearing a daughter named Ouka. The mingling of human and demon blood triggered paranoia, becoming the origin of Hinamizawa Syndrome. To quell unrest, Hanyū accepted blame for the villagers' sins and was sacrificed during the first Watanagashi festival. Ouka, directed by Hanyū, cracked her horn with the sacred sword Onigari-no-ryuuou to end her life. After death, Hanyū persisted as an incorporeal spirit, watching over generations until Rika's birth as the eighth Furude heir finally allowed her to interact with a human again.

Personality-wise, Hanyū is notably timid, prone to nervous muttering ("au, au"), and pessimistic, often discouraging Rika's optimism to prevent repeated disappointment. She harbors deep guilt over historical events and the suffering caused by Hinamizawa Syndrome, leading her to follow afflicted individuals while apologizing—manifesting as the "footsteps" heard during paranoid states. Despite this, she displays maturity when invoking her goddess persona, confronting adversaries like Takano or the Mountain Dogs, and can strategically manipulate others using her childlike appearance.

Her abilities include initiating time loops, allowing Rika to reset timelines upon death, though her power waned over centuries, reducing the reset window to only two weeks pre-death. She can switch between corporeal and incorporeal forms, stop time, teleport, fly, use mind control, and temporarily alleviate Hinamizawa Syndrome. Her cracked horn initially caused Rika's incomplete memory retention during loops. In later arcs, she wields the Onigari-no-ryuuou and channels "Fragments" for combat.

In *Rei*'s Saikoroshi-hen, Hanyū communicates with Rika via a spirit orb after Rika is displaced into a new fragment. She reveals this world's Furude lineage lacks an eighth-generation heir, meaning its Hanyū has vanished. Guiding Rika's return requires extracting a "fragment" from her mother, involving lethal sacrifice. After Rika succeeds, Hanyū implies the experience was an orchestrated lesson on appreciating life.

Post-Matsuribayashi, Hanyū fades from the human world, believing the miracle achieved. In *Gou*/*Sotsu*, she reappears weakened in the Sea of Fragments when Rika is forced back into looping. She repairs her horn to restore Rika's death memories, sacrificing herself to confront Eua—a being claiming to be her "original" self, revealing Hanyū split from Eua after a horn injury. Hanyū battles Eua to protect Rika, ultimately damaging Eua's horn and reclaiming agency. The manga *Meguri* alters this slightly: Hanyū remains corporeal longer but vanishes after empowering Rika with memory restoration.

Relationships define her actions: she acts as a mother figure to Rika, teaching her skills like cooking, though their bond strains over time. Their senses link, allowing shared physical experiences. She also connects with Rena Ryūgū, who senses her due to past spiritual encounters. Eua's introduction recontextualizes Hanyū's existence as a fragment of a higher entity, adding complexity to her origins.