Kuraki Tatari no Mori de

In the year of 1991…
Kamo Akinori, a student at Tokyo’s private W University, is working on his graduation thesis about the “Sekkan Politics” of the Heian period. As part of his fieldwork, he decides to spend his summer vacation in W Prefecture with a group of friends from his folklore seminar: Abe Yasuchika, Nakamiya Seiko, Horikawa Itsuki, and their chaperone, Sanjou Misao, a researcher from the seminar. To make things even livelier, Yasuchika’s younger sister, Abe Otoha, tags along uninvited.
On the surface, the trip is for research, but the group is really just looking forward to a fun camping getaway. However, things take a turn when they meet locals struggling with strange, supernatural phenomena tied to the area.
One is the owner of a resort hotel under construction, frustrated that ghostly occurrences are delaying the project. The other is the construction site supervisor, who’s struggling to keep workers on the job as they grow increasingly terrified of the unexplained events.
The group initially brushes it off—they’re not exactly ghostbusters, after all—but when both parties offer free lodging and meals in exchange for help, they figure it’s a win-win. They can enjoy their vacation while making progress on their fieldwork.
But as strange occurrences start happening around them too, the group begins to feel the pressure. Little do they know, this is only the beginning of a far more terrifying ordeal…

[Translated from dlsite]