Kowaku no Toki

Mibu Kyousuke runs a small detective agency along with his assistant Momono Momoko. They only take on cases that interest them, leading a seemingly peaceful life. However, Kyousuke is haunted by nightmares of an unknown girl being violated. One day, they receive a request to find a missing person. The area related to the case is infamous for mysterious disappearances, known locally as "spirited away" incidents. Intrigued, Kyosuke accepts the case and ventures into the deep mountains. What awaits him there is a sinister mansion filled with conspiracies and a beautiful girl who looks strikingly similar to the one in his dreams...

[Translated from the official site]