Kimiyoshi Aki is the mother of Kimiyoshi Haruko and the grandmother of Kimiyoshi Natsumi. She's a native of Hinamizawa and also the person who triggers the events of Onisarashi-hen.
Kimiyoshi Aki is a former resident of Hinamizawa, and just like the other old Hinamizawan people, she blindly belives in Oyashiro-sama. Because of her son-in law's job, she had to move from her hometown along with her family. She always looks after Natsumi and daily prays to Oyashiro-sama.
(Source: Higurashi No Naku Koro Ni Wiki)
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