Sachio Sadahama lives with his wife, Sae Sadahama, on Shio Island in the Seto Inland Sea. He is a relative of Ikuko Miyaura and her daughter Momo, who come to live on his estate after the death of Momo's father. The estate includes an orchard tended by Sachio.

Within the estate's attic, Sachio keeps a rare picture book about goblins and yōkai, inherited from his father. This book gains significance when Momo discovers it.

Sachio's orchard faces damage when fruit is stolen by three manifested yōkai—Iwa, Kawa, and Mame. After Momo reports the ransacked orchard, Sachio provides her key information about these beings. He reveals they were originally gods transformed into their current state as punishment for breaking divine laws.

Beyond these events, Sachio's role involves offering familial stability and local knowledge. He and Sae form part of the household supporting Momo and Ikuko during their transition to island life.