Hanyuu is the mysterious “transfer student” in Matsuribayashi-hen. She has a pair of dark colored horns on her head, one of which is chipped slightly (however, no one seems to notice or mention them, with the exception of Takano, who calls her a “monster”).
In fact, she has appeared to Rika all her life, but only in Matsuribayashi-hen and Miotsukushi-hen did she gain the power to interact with others, posing as a distant relative of Rika’s and given the name “Hanyuu Furude.” Like many of the characters, she can be frightening when angered, and with her spirit-like nature, her appearance can change with her mood until she takes a physical form.
She is very meek and often makes the noise “Au au, au au…” when she is nervous or uncomfortable, or sometimes while trying to make a point. She also tends to end her sentences with nano desu (なのです?, lit. “it is so”).
She dislikes alcohol and kimchi, which Rika imbibes in large amounts as punishment when she finds Hanyuu annoying (as both Hanyuu’s and Rika’s senses are linked together). She mentions that she is a “being above humans” after being sacrificed to atone for the sin of humans, while both Rika and Takano describe her as a kind of deity.
Rika refers to her as “Oyashiro” when talking with others (evident from Shion’s chat with Rika in Meakashi-hen) but does not personally think of her as Oyashiro; instead, she sees her as a close friend.
In Higurashi no Naku Koro ni Rei, Hanyuu tells Rika that she was sacrificed to atone for the sins of the people of the village, and Hanyuu asked Ōka Furude (Hanyuu’s own daughter and Rika’s ancestor) to kill her and then make the village a better place.
She is the one responsible for the eternally repeating June 1983, which she created in order to save Rika from being murdered.