In a parallel world where Japan hasn't privatized its railways, Naoto dreams of being a train conductor for the Japanese National Railways. He luckily manages to snag a job as a trainee for the Railways Security Force. However, Naoto’s expectations are quickly derailed when he finds that he has trouble telling who’s crazier- his coworkers or the criminals he’s supposed to catch! But when RJ, a sinister group, appears to seize control of the JNR, it’s up to him to get things back on track.
Naoto's dream of working for the JNR begins at the training academy, where he meets his soon to be friends and co workers. A purse snatching tests the groups' mettle early on.
After complaining about the lack of action involved with their line of work, Sakurai finds herself in an explosive situation as she and Naoto must find a bomb before it goes off in the station.
Naoto runs into his old friend Sasshi, who happens to also go to Kiryu Railway High School. Later, Sasshi's friend goes missing, and Noato and the Railways Security spring into action!
Popular idol Kashima Noa will hold a special concert at the beach as part of a JNR Event. When a suspicious letter is sent to her manager, K4 is appointed to protect her during her stay.
The railway bomber is revealed to have an accomplice still on the loose, and Sakurai vows to apprehend him, with Naoto as part of her team.
During their suspension, Naoto receives a threatening letter in the mail, which prompts Koumi to suspect foul play. Sakurai spots them running from something, and gives chase to find out.
Naoto and the rest of K4 make their way to Karuizawa for some advanced training. Sakurai uncovers the real reason Naoto is in the security force, and their friendship is strained as a result.
A mudslide has caused a delay in schedule for a train and it's passengers, one of who is carrying life saving organs. It's up to K4 to deliver the goods before time runs out.
With time running out, Naoto and K4 begin to exhaust their options for slowing their train. Dangerous tunnels and uneasy tracks remain, will they make it in time...and in one piece?
A foreign Prince with a penchant for trains is coming to town, and K4 is assigned protection detail. As Sakurai trails a suspicious character, the train leaves the station with the Prince and the rest of K4 on board.
Naoto and his team manages to outwit the attackers on board, but discover that the train's controls have been damaged in the aftermath. With time running out and their train barreling faster down the track, Naoto will have to think quick to save his team and the passengers.
On their way back from cleaning up the aftermath of their last mission, Naoto and Iida take a ride on an old reliable KiHa 381. What is supposed to be a routine trip turns a corner when Naoto hears something strange coming form the engine room...