Yanagi belongs to the treefolk, a sentient species resembling humanoid plants characterized by olive-colored hair and eyes. She holds the position of elder within her people's community in the capital city. Yanagi wields deep knowledge of the catastrophic history that altered human physiology, causing spontaneous combustion near fire, and the origins of fire fiends whose blood became humanity's alternative fuel, bottled lightning. She imparts this lore to protagonists Touko and Koushi during their visit, detailing how mismanagement by divine clans shaped the world's current state. Yanagi further explains the mythology of Tokohanahime, the fire goddess who forged the first hunter's sickle and prophesied a "lord of the fire hunters" destined to confront the returning millennial comet, the Flickering Flame. This prophecy is central to the treefolk, who believe the comet's anger threatens planetary destruction unless appeased by the chosen lord. Later, Yanagi is found at a factory by Koushi and his companion Mr. Hitoo, alongside Hinako. She informs Koushi about Kunugi's activities and a giant pit near the capital, implicating him. Revealing her treefolk companions are scattering due to escalating dangers, she advises Koushi to flee. When asked about another's whereabouts, she directs Koushi to Kunugi. Accompanying Koushi, Hinako, and Mr. Hitoo towards the divine palace, Yanagi witnesses Kunugi's actions firsthand. During this confrontation, she suffers a fatal incident. Her body, along with Koushi's inherited fire hunter sickle, is later seen embedded within Kunugi's roots. Yanagi's role bridges ancient mythology and unfolding events, providing critical exposition about the world's state and the prophesied savior while demonstrating loyalty to her treefolk community until her demise.