The series aired in Japan between April 7, 2002 and March 30, 2003, with an English-language version, produced by Sensation Animation, airing in North America between September 9, 2002 to July 14, 2003. It was the last season to use the Digital Monsters title as subsequent series, beginning with Digimon Data Squad, began using unique localized titles.
Long ago, a group of ten Digimon sacrificed themselves to defeat an ultimate evil that threatened the Digital World. These Ancient Warriors created artifacts from their data, the twenty "Spirits" (ten Beast spirits and ten Human spirits, one of each for each element), before leaving the Digital World in the care of the three Celestial Digimon. However, one of the three, Cherubimon begins a reign of terror. To counter this, the Celestial Digimon Ophanimon summons five children (Takuya, Koji, Zoe, Tommy and J.P.) from the human world into the Digital World via the train-like Trailmon.
There, these five Digi-Destined find their respective Human Spirits and "Spirit Evolve" into Digimon, the Legendary Warriors. However, while finding their respective Beast Spirits, the five find themselves hunted by five other Legendary Warriors that serve Cherubimon (for five of these spirits were given to the care of Cherubimon before his corruption). After they defeat four of them (JP destroys one, another loses his Beast Spirit to Koji and is destroyed by Duskmon for being useless, Zoe destroys another and Takuya destroys the last one), Koji Minamoto discovers that Duskmon, the fifth evil Legendary Warrior, is really his twin brother Koichi Kimura. With Takuya Kanbara's help, Koji is able to free his brother, and Koichi restores the Spirits of Darkness to their true forms and joins the team as the true Warrior of Darkness, Löwemon.
The DigiDestined arrive at the Rose Morning Star and find Ophanimon, trapped, who teaches them of Cherubimon's past and the war. Cherubimon then shows up and fights the lot. Proving to be too powerful for the DigiDestined, he steals all of their D-Tectors except Zoe's, who is still fighting to the very end as Zephyrmon. Just as Cherubimon is about to destroy Zephyrmon, Ophanimon breaks out of her imprisonment and sacrifices herself to save Zephyrmon and retrieve the others' D-Tectors. The children then discover that Ophanimon upgraded Takuya's and Koji's D-Tectors with her last bit of strength to allow them to Unity Spirit Evolve into EmperorGreymon and MagnaGarurumon, respectively. After using these new evolutions to defeat Cherubimon, the DigiDestined learn that the true mastermind is the very evil the Ancient Warriors sealed away within the Digital World's core, Lucemon.
So now the six DigiDestined must try to defeat the two Royal Knights, Dynasmon and Crusadermon who were sent by Lucemon to scan all of the Digital world's data to complete his rebirth. Ultimately Takuya and Koji succeed in defeating the two evil knights as well as three SkullSatamon (who also serve Lucemon), but not before they destroy and scan the whole digital world and free Lucemon (who scans the Royal Knights after the DigiDestined defeat them, allowing him to evolve to a more powerful form than he was before). At this point, after defeating Takuya and Koji as EmperorGreymon and MagnaGarurumon, Lucemon destroys the Digital World's moons. He then began opening a portal to the real world: a portal that leads to the underground train station in which the DigiDestined were brought. He is confronted by the Digidestined who try to attack him with a multi hit tactic, fighting together as a complete team. However Lucemon ends up killing Koichi (who sacrificed himself to save the others). Forming the ultimate Legendary Warrior Digimon Susanoomon by combining all the spirits in Takuya and Koji, Lucemon is defeated and scanned. However, all of his evil transforms into another form of Lucemon, one of pure evil, which tries to go to the real world. Having almost given up, the spirits of the Ten Legendary Warriors come to life, along with the spirits of Ophanimon, Cherubimon and Seraphimon, giving the kids new hope. Together, they all form a seemingly more powerful Susanoomon, and defeat and ultimately destroy Lucemon (at least the evil part of Lucemon) once and for all, giving the Digital World its data back, ultimately restoring its true form.
The children go back to the real world and find that an hour hasn't even passed since they left (only a 1/2 hour at most). They find Koichi, who they discover was only in the Digital World for having been in a coma by falling down a flight of stairs. He then wakes up when Koji arrives and the kids' D-Tectors heal him before turning back into cell phones, leading everyone into living happily ever after by having the events of the Digital World change them forever.
The series, produced by Toei Animation, aired in Japan for 50 episodes on Fuji TV between April 7, 2002 and March 30, 2003. An English-language version, produced by Sensation Animation and recorded by Studiopolis, aired in North America on UPN, ABC Family Channel, and YTV between September 9, 2002 and July 14, 2003. The dubbed version featured an original soundtrack, original sound effects, changes to character names and edits pertaining to violence and other scenes thought to be inappropriate for younger audiences. The series was originally scheduled to air on Jetix in the United Kingdom (following on from Digimon Tamers). However, the series was put on hold and was never broadcast by the time the channel ended in August 2009. New Video Group released a complete DVD box set of Frontier on September 10, 2013 in the US. Following previous releases, it uses the English dub and includes a character book.
The opening theme song used for the series which was first broadcast in Japan is the song "FIRE!!" by Kōji Wada. Two different songs were used for the end themes, one for the first twenty-six episodes, and the other which covered the rest. For the first ending theme, the song "Innocent ~Mujaki na Mama de~" (イノセント〜無邪気なままで〜, Inosento ~Mujaki na Mama de~, "Innocent (Remain Innocent)") by Kōji Wada was used. The second ending theme song was entitled "an Endless tale" which was done by Kōji Wada and Ai Maeda. In addition to the theme songs four insert songs were used for the series these include; "With the Will" by Kōji Wada, "The Last Element" by Ayumi, "Salamander" by Junko Takeuchi, and "Oreta Tsubasa de - With Broken Wings" by Spirit Shinkers. The English adaptation of the anime uses a single theme song called "A World for Us All" by Christopher Horvath. The end theme features a remixed version of the opening theme. In addition to the single theme song, one insert song entitled "Digivolution" by Deddy Tzur and Inon Zur is present.
This audio drama takes place during and after their adventures in the Digital World. The children find a mailbox and decide to write letters to the people they care about, expressing things that they normally cannot say.