Naraku no Shiro Ichiyanagi Nagomu, Nidome no Junan

Following his last case, detective Ichiyanagi Nagomu accepts an invitation from his friend Hiori to visit Ruroi Castle — a remote European fortress accessible only by rope bridge, hidden in a deep valley. Over dinner, the current owner shares the castle's history: an ancestor devoted to black magic who summoned a demon by sacrificing youths, then sealed the possessed victim inside the valley walls. A mother who entered to find her son was never seen again, and locals say her ghost still wanders the halls. When darkness falls and cuts the castle off from the outside world, the guests feel the weight of that old evil all around them.