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.

Having qualified for on-the-job training, Naoto is assigned to K4, the Tokyo Central Railway Security 4th Guard Team. Waiting for him there are his partners from JNR Central Academy: Aoi, Haruka, and Sho. They immediately set about their work at Tokyo Station, but as if being teamed up with the gruff Aoi didn't worry him enough, Naoto is increasingly anxious as he watches the Tokyo Public Security Mobile Police set out on a mission.

Naoto and K4 head toward Yokokawa as the rain plummets down. Haruka says the track from Usui Bridge No. 3 to Yokokawa should be safe since it's regularly maintained for the opening of the Usui Abt Railway, but the downgrade is steep, they can't slow down, and the narrow tunnels make it difficult to handle curves... They're in a serious pinch when Iwaizumi takes action!