The Sonozaki Family (園崎家・ Sonozakike) also known as the Sonozaki Group (園崎組・ Sonozakigumi), is one of the "Three Great Families" of Hinamizawa that are believed to have the highest concentration of the demon bloodlines and to have long been the enforcers of the traditional practices and customs of village. Research done by Takano Miyo and contained in Document No. 34 indicates that the Sonozaki were originally the weakest of the houses, This same document notes they are widely believed to be responsible for the strange happenings that occur around the Watanagashi Festival.
Currently the Sonozaki holds a great deal of influence both inside and outside the village. Under the leadership of Oryō, the Sonozaki directed the movement to stop the dam construction five years before the start of the series. They are believed to have been responsible for kidnapping of the grandson of the Minister of Construction, having returned him only after the dam project was put on indefinite hold. In Minagoroshi-hen, is revealed that there are Congressmen from the Prefecture and Municipal Governments in the Sonozaki Family.
The Sonozakis are portrayed as being in some ways similar to traditional yakuza, with a large number of people in their service. Akane's husband and the father of Mion and Shion is the "boss" (親分・oyabun) of the local yakuza organization.
The main family lives in a large and traditional house near the river, complete with a lavish garden. There is also an ancient secret torture chamber/dungeon, and an extremely deep well for the disposal things not wanted found.
Traditionally the first-born child inherits the roll of the head of the family. Because Oryō's daughter Akane married someone unapproved, Oryō stripped her of the right to inherit in favor of her daughter. There is speculation that Oryō did this to "save face" after losing a kendo duel with her daughter over the matter; both Akane and her husband sit with, support, and advise Oryō. Regardless, Akane's first-born was to be next in line. Since she gave birth to identical twins, by tradition the older twin woud inherit the succession and receive the demon tattoo, while the younger would have been strangled or otherwise left to die. While the anime and manga depict an enraged Oryō approaching the youngest infant with her hands as if to strangle her, clearly she did not, and why she changed her mind is not revealed. One of the twists of the series is that the younger twin switched places with her older sister so she could spend a fun day with their mother while she spent what they expected would be another dull day observing grandma handle family affairs. Instead, that was the day the heir received her tattoo. Therefore, the marked girl and heir viewers know as Mion is actual the second-born Shion, and the "younger twin" Shion is actually the older sister Mion. Only the twins themselves seem to be aware of this.