Psycho Mystery Series 'Sin -Tsumi-'

When he came to, he found himself collapsed deep in the mountains.
Judging from the business card he was a reporter named Kogami Yato, but he had only a vague memory of where or why he was here.

According to Aida Mamoru, the young man who helped him, they were in the mountains of Aomori, near Karubarikan, a Western-style mansion built by the president of a major corporation. Apparently, a valuable painting was being auctioned at the mansion that day, and the young man had been invited as a history student.
Hoping to find clues to his lost memories, the protagonist decides to visit the mansion with Aida, but...

[Translated from G-Mode official page]