Sonozaki Oryou

She is the head of the Sonozaki family, one of the Three Families, and the grandmother of Mion and Shion.

She is greatly feared as the heir to the demon.

Because of the anti-dam movement, there is a rift between her and the Houjou family.

Spoiler

The Sonozaki family's involvement in Oyashiro-sama's curse and the 1978 kidnapping is a lie. Oryou implies that the Sonozakis are behind everything to make them seem more powerful and influential than they already are.