Minare and Mizuho join Kureko on his research trip to the secluded mountain village of Wassamu, where he hopes to gather ideas for a mystery novel. While their local guide, Hokakushi, offers some insights into the area, Minare can barely stifle her boredom—a worry quickly forgotten when the three radio employees find themselves trapped in an old underground canal! What could be illuminated by the light at the end of the tunnel?