Takayama Naoto is a high school second-year who dreams of being a train conductor. In hopes of getting a job with Japan National Railways, one of the most stable businesses in Japan due to government support, Naoto has applied to an on-the-job training program for students.

Prince Bernina of the small Mediterranean kingdom of Atella has arrived in Japan to attend a sister city ceremony in Sapporo, and the K4 members are appointed to guard and guide him on his way there. Naoto and the others are about to board the Hokutosei 3 at Ueno Station when Aoi contacts Naoto and tells him she's pursuing a suspicious man who was watching the platform.

After seeing the others back to Tokyo while they cleaned up the aftermath of the Hokutosei incident, Naoto and Iida wait at Aomori Station. The engine that will pull their train to Tokyo is the KiHa 381, equipped with a pendulum-style, diesel-fueled gas turbine engine. Shortly after they depart, Naoto hears a strange sound and can't shake the feeling that something isn't right.