園崎 詩音 Sonozaki Shion
Shion is Mion’s identical twin sister. She currently resides in Okinomiya rather than Hinamizawa. Shion and her sister often switch places sometimes making it rather difficult to tell the difference between the two. They’ve done this from a very young age which led to Shion being mistaken for Mion and passed up as next in line for family leadership. After the massive switch Shion and Mion permanently took over each others identities.
Shion was sent, by the Sonozaki family, to a private boarding school. She escaped however and returned to her home town living with Kasai even though she knows its against the wishes of her family. Shion and Mion still maintain a close relationship despite all of this.
Shion fell in love with Satoshi Hojo and blames the The Families of Hinamizawa for his disappearance. This is shown through both of the arcs when Shion is affected by the syndrome, the latter of the arcs being her point of view. It is also later revealed in the second season of the show that Satoshi didn’t vanish really, the families took him underground and put him into a coma so that the syndrome didn’t claim his life.