Kokushi no Shima

Kokushi no Shima (黒祠の島, lit. "Kokushi Island") is a manga series written by Fuyumi Ono and illustrated by Kotetsuko Yamamoto.

Plot
Two friends investigate the disappearance of a writer on a small island, which has been largely cut off from the mainland since the fall of the Shinto during the Meji era. They stumble across several strange occurrences, such as a naked female corpse hanging upside down on a tree during one stormy night. Locals speak of old-standing traditions, folk rituals and superstitions, but after more bodies were found, Shiho and Tsuyoshi wonder if there's a serial killer among the locals.