Ghoul.

This dark fantasy depicts the horror that befalls a group of young people who are gathered in a Western-style mansion deep in the mountains by an unknown entity. Kota and Yosuke were best friends, but a certain incident caused them to drift apart. One day, they are each invited to the mansion deep in the mountains and reunite, only to find that they, along with other young strangers, have been gathered there. The mansion's butler, Moriyama, appears before them and tells them they cannot leave unless they confess to their master.