Forest Of Drizzling Rain

After the sudden death of her parents, a young woman named Shiori Kanzaki find a picture of a man that she believes to be her grandfather, and travels to Azaka Village, where he was apparently from, in hopes of meeting him. However, when she arrives she instead finds that the tiny village has a museum that she realizes she lived in as a young girl. There she meets Sakuma, a middle school girl who tends to get herself in trouble, and Suga, the strange manager of the museum who only communicates in written memos. Suga grudgingly allows her to stay at the museum for awhile and research her family. But there is a legend in the village of "Kotori Obake", a demon woman who abducts children who go into the nearby forest. How is this story connected to Shiori's past, and why does she hear voices calling her, commanding her to "Come fulfill the promise"?