Hanyū was once known as the demon god of Onigafuchi (Hinamizawa) under her true name, Hainiryūn Ieasomūru Jieda. She travelled with her clan to the Onigafuchi Swamp and tried to coexist with the human villagers there, but the Furude priest refused to cooperate. However, Furude Riku, the heir to the Furude shrine and inventor of the nickname "Hanyū", fell in love with Hainiryūn and married her. They had a daughter named Furude Ōka, the first in a long lines of humans to carry demon blood. When the villagers of Onigafuchi became violent towards Hainiryūn's clan and could no longer tell who was a demon and who was not, they started to suspect and blame each other. Because of this, Hanyū chose to become a sacrifice to atone for the villagers sins. She asked Ōka to kill her in what became the first Watanagashi ceremony, and by doing so, she 'buried' the villager's sins along with her.
Added by HiMizaWa
Quiet, timid, and polite, Hanyū is a sweet and innocent girl, despite her tendency to refer to herself with the pronoun "boku", which is generally reserved for boys. She is easily intimidated or frightened, and will whimper "Au au, auauau…" when upset or excited. When angry however, her eyes turn red and her voice becomes stern and mature like that of a god.
Hanyū is extremely loving and carries a lot of guilt for the suffering she has caused Rika's friends. In addition, she often feels helpless or despairing due to her inability to influence the world around her in her spiritual form. All she feels she can do is apologize for her uselessness in protecting the ones she loves, which led to her habit of following those who are about to fall into paranoia or die and repeatedly saying "Gomen nasai" (I'm sorry). She is the source of the footsteps, voice and sense of being watched that Ryūgū Rena, Hōjō Satoshi, and other characters under the influence of the Hinamizawa Syndrome notice throughout the series.
Hanyū is also very pessimistic, often telling Rika not to get her hopes up about the newest world, as every time she does, she only ends up getting hurt and disappointed. Instead, she encourages Rika to wait patiently for a fortunate world to come. She hopes that by dispiriting Rika, she can prolong Rika's mental life-span. Despite Rika's desperate desire to escape her fate of being killed, Hanyū seems content with repeating the worlds over and over, as long as she gets to stay by Rika's side; she is secretly happy that she gets to spend more time with Rika than anyone else.
Hanyū likes cream puffs and sweets, which she tastes through Rika, whom her senses are linked with. She also likes stalking her friends, occasionally causing their paranoia to grow stronger, and some of them outright mistake her for the vanished Satoshi, such as Keiichi in Tatarigoroshi-hen, and Sonozaki Shion in Meakashi-hen. She wants to join the club, and unbeknownst to the members, usually watches their club activities.
Hanyū dislikes spicy food and alcohol, both of which Rika likes, and often uses to punish Hanyū when she is being annoying. Contrary to the village's image of Oyashiro-sama, Hanyū hates violence and suffering, and is devastated by the horrific acts that are committed in her name. Because of this, she expresses a strong dislike for Takano, who is only attracted to the legend of Oyashiro-sama due to its bloody history. When the topic of Oyashiro-sama arises, Hanyū is especially irritated and discouraged when she hears her name used as a name of punishment and violence, declaring numerous times that she would never curse or punish anyone through torture nor "demoning away" (however, Rika does note that Hanyū loves to stay in the Saiguden, which is full of torture tools, because according to Hanyū it makes her feel "at home"). In scenes where Takano enters the Saiguden and revels in the violent history of Onigafuchi Swamp in front of the statue of Oyashiro-sama, Hanyū becomes very upset and repeatedly stomps on the floor in agitation. Since anyone at LV3 or higher of the Hinamizawa Syndrome can sense Hanyū's presence, Tomitake Jirō (LV3) and Shion (LV4) were able to hear "a child jumping up and down on the ground" in Minagoroshi-hen, Watanagashi-hen and Meakashi-hen. The jumping noises were Hanyū stomping the floor and exclaiming, "Stop it, stop it! I would never do such a thing, I never asked anyone to torture people!"
Hanyū's appearance in Higurashi no Naku Koro ni Kai
Added by SlavEliseev
Hanyū's first form appears to be a floating, translucent young girl with purple hair, violet eyes, and a pair of black or dark purple horns on her head (the left one is chipped slightly). When angry or channeling her god powers, her eyes turn a glowing red. In this spirit form, she wears an outfit reminiscent of one worn by a Shinto shrine maiden, with red hakama (long, split trousers), a white haori (kimono jacket), and a pair of long, pink furisode-like sleeves.
The second form that Hanyū takes is her visible form, which is physically identical to her ethereal form except that she can no longer float and she is solid rather than transparent. Here, on her school days, she wears a school outfit with a red plaid skirt, a short sleeved white blouse, a blue vest with a blue bow, white socks and brown shoes. During her free days, she wears a pink jumper similar to Rika's dress, differing in that the jumper has pockets, its straps are thicker and have buttons, and has no ribbon. In this form, her horns remain intact.
Hanyū expresses a dislike for her horns in one of the TIPS, acknowledging them as ugly. In the sound novels, people are aware of her horns, and Maebara Keiichi asks her about them, thinking they are toys. Once Keiichi sees that Hanyū is sensitive about her horns, he apologizes, and the club members tease Keichii by saying he has "a horn between his legs" and reassuring Hanyū that there's nothing wrong with her. Takano Miyo, however, upon seeing them refers to Hanyū as a monster, which only further ignited Hanyū's hatred for Takano. Even though Hanyū possessed this hatred for Takano, she sacrificed her life to save Takano's in Miotsukushi-hen.
During an early episode of the Higurashi no Naku Koro ni Kai anime, Hanyū appears in a thin-strapped pale pink sun dress. There are bows on tow of the straps and on the front of the dress, and the bottom is tinged with lace. She is only seen once in this outfit.