Runaway Locomon is the sixth Digimon film, and is set after the finale of Digimon Tamers.
Six months after the D-Reaper was destroyed, the Tamers are planning to throw Rika a surprise birthday party, but Rika finds out. Suddenly a train-Digimon named Locomon begins to race around the tracks, causing havoc. The Tamers respond to this, as TakatodigivolvesGuilmon into Growlmon to stop the train Digimon but fails as Takato, Rika and Renamon get on it in an attempt to slow it down. The others, excluding Suzie, use a freight train to catch up with Locomon.
Yamaki takes over command of the rail centre, noticing that Locomon's path is creating a distortion in the digital field—in other words is creating a very large digital zone. He has the railroad workers manually divert the tracks at station 9 to redirect Locomon back to the Digital World.
It is then discovered that Locomon was being controlled by Parasimon. In the end Gallantmon destroys the Parasimon that was controlling Locomon but not before it sends a signal to start an invasion. Gallantmon, MegaGargomon, Sakuyamon, Justimon, Guardromon, MarineAngemon and Beelzemon Blast Mode fight the invasion but are seriously outnumbered. They finally win when Takato's determination causes Gallantmon to mode change into Gallantmon Crimson Mode, who then destroys all of the Parasimon in one shot with his Crimson Light attack. Locomon returns to the DigiWorld and the entire gang attends Rika's birthday party. Kazu asks Rika to sing, since Rika sung a song for her dad in a vision while she was being controlled by Parasimon. Rika then leaves, with the movie ending with her watching the sunset, singing the last line of her song in her head: "You promise that we'd stay for the sunset".
Kenta: "Uh, guys, does that look normal to you?" Terriermon: "I'm not sure...DO HUGE EYEBALLS FALLING FROM THE SKY LOOK NORMAL TO YOU?!?!"
Some of the Biomerging sequences were edited, as well as Gallantmon's graphic impaling of the main Parasimon's eye, MegaGargomon blowing the Parisimon into pieces, and Gallantmon impaling a Parasimon and tossing it at another.
At the end, when Suzie and Rika's mom sing, in the Japanese Version, Suzie sings a part of "The Biggest Dreamer" (Opening of Digimon Tamers), and Rika's mom sings a part of "My Tomorrow" (1st Ending of Digimon Tamers).
The music for Spirit Evolution from Digimon Frontier was used for the DigiModify and Digivolution sequences. The dub-altered Digivolution text on the Digivices look noticeably different and less digital from its appearance in all other dubbed Tamers media, even different in how it appears across the screen, doing so in a sweeping manner as opposed to each letter flashing.
Runaway Locomon was dubbed into the English language around three years after the Japanese broadcast of the film. However, as the production rights had been transferred to Disney from Fox (following the demise of the Fox Kids block, on which Tamers was the last season of Digimon broadcast on that network), the film's title song was replaced with the theme song for the English version of Digimon Frontier, as Disney didn't possess the rights to use the theme song that was licensed to the first three seasons on Fox. However, it reunited much of the English cast of Season 3.
Chiaki Konaka states in his character notes (for Rika) that he "was not consulted" on Runaway Locomon, which possibly explains certain continuity errors. On this he also says:
"However, ...Mr. Tetsuharu Nakamura [the director], [who was] an assistant director of the TV series... [and] Mr. Hiro Masaki,... a regular writer for the series... paid a great deal of attention to the psychological aspects of the series when completing the movie... I am very grateful to them for boldly illustrating the parts of Rika's family life that the TV series never explored."