is the fourth anime television series in the Digimon franchise, produced by Toei Animation. Unlike the previous series, the main characters can merge with ancient spirits known as the "Legendary Warriors" to become Digimon themselves.
The series aired in Japan from April 2002 to March 2003. An English-language version, produced by Sensation Animation, was broadcast in North America from September 2002 to July 2003 as the fourth and final season of Digimon: Digital Monsters.
In the events prior to the series, ten Digimon creatures from the "Digital World", a parallel universe originated from Earth's various communication networks, sacrificed themselves to seal Lucemon. These Digimon, collectively known as the "Ten Legendary Warriors", created artifacts from their data: the twenty "Spirits" (ten Human and Beast Spirits for the elements of fire, light, wind, ice, thunder, earth, wood, water, metal and darkness), before leaving the Digital World in the care of three Celestial Digimon, Ophanimon, Cherubimon and Seraphimon. When Cherubimon betrays them, Ophanimon summons six children from the human world into the Digital World to become the "DigiDestined".
Takuya, Koji, Zoe, J.P., and Tommy are among several children who receive a text message inviting them to board a train at Shibuya Station. The train brings them to the Digital World. While exploring, the five gain the ability of Spirit Evolution, where they are able to transform into ancient Digimon warriors and meet two guided Digimon named Bokomon and his dim witted sidekick, Neemon. In addition, their cell phones have turned into a type of Digivice (digital device) known as a D-Tector, which they can also purify defeated Digimon by scanning them.
While exploring, the Legendary Warriors learn from Seraphimon that he, Ophanimon, and Cherubimon once maintained order among the human and beast-type Digimon, until Cherubimon became corrupted and urged the rest of the beast-type Digimon to engage with the human-type Digimon in a war. During this time, the Legendary Warriors are forced to fight five other ancient Digimon warriors, one of which Koji learns is his estranged twin brother, Koichi, who was corrupted into Duskmon. Koji manages to purify Koichi, allowing him to join them on their quest to defeat Cherubimon. They rescue Ophanimon while Cherubimon attacks them, but she sacrifices herself to save them and upgrades Takuya and Koji's D-Tectors with the last of her strength to allow them the ability of Unity Spirit Evolution.
After defeating Cherubimon, the DigiDestined learn that Lucemon is sealed within the Digital World's core, and a guide named Baronmon, warns the six Digidestined that the prophecy is that Lucemon will be revived. Two Royal Knights, Dynasmon and Crusadermon, are summoned by Lucemon, and steal all of the world's data to awaken him. The kids attempt to stop the evil knights from scanning the entire digital world, but they fail as they finally free Lucemon. After Takuya and Koji defeat the knights, Lucemon kills them for their failure and absorbs their data to Digivolve into his Chaos Mode. Koichi is revealed to be a digital shade - his physical body is unconscious in the real world after a dangerous fall. Lucemon destroys Koichi's digital form and absorbs his data, which enrages Takuya and allows all the spirits to combine into the ultimate Legendary Warrior Digimon Susanoomon. Though initially defeated, Lucemon Digivolves into his Shadowlord Mode, and arrives in the real world. After reviving Ophanimon, Cherubimon and Seraphimon, Susanoomon successfully destroys Lucemon, restoring the data and the Digital World. The children return to the real world and realize that an hour did not pass, and save Koichi by using the power of their D-Tectors, which then revert into cell phones. Takuya and his friends then embrace their future.
These are the Human Spirits and the Beast Spirits of the other Legendary Warriors that were possessed by Cherubimon and given to his unknown minions. Duskmon was originally part of this group. Each one was defeated by the DigiDestined and freed from their control. During the fight against the Royal Knights, the DigiEggs that were originally associated with these Human and Beast Spirits were briefly reunited and helped to fight off the Royal Knights. Also, the Human and Beast Spirits were part of Susanoomon's final attack on Lucemon Larva.
The Royal Knights are servants of Lucemon who collect data to send to his imprisonment. Though both of them were slain by EmperorGreymon and MagnaGarurumon, their data was absorbed by Lucemon before they can be purified.
Toei Animation announced the production of a fourth Digimon series in February 2002 and was set to start in April, after Tamers. Digimon Frontier was conceived by Fuji TV's Go Haruna, Yomiko Advertising's Kyà Âtarà  Kimura, and Hiromi Seki. The series was directed by Yukio Kaizawa, who had previously worked on some Bikkuriman shows and certain One Piece episodes. It was chiefly written by Sukehiro Tomita, while character designs were done by Katsuyoshi Nakatsuru.
Digimon Frontier aired in Japan on Fuji TV from April 7, 2002, to March 30, 2003. The show's opening theme song is "Fire!!" by KÃ Âji Wada, which peaked at #75 on the Oricon Weekly Singles Chart. The ending theme songs are by Wada for the first half and "An Endless Tale" by Wada and AiM for the second half. The insert songs featured in the show are "With the Will" by KÃ Âji Wada, which served as the Spirit Evolution theme, and "The Last Element" by Ayumi Miyazaki, which was the theme song for Unified Spirit Evolution.
An English-language version, produced by Sensation Animation and recorded by Studiopolis, aired in North America as the final season of Digimon: Digital Monsters. It aired on UPN's Disney's Animation Weekdays block and Canada's YTV between September 9, 2002, and July 14, 2003. Frontier was part of a package deal with Digimon Tamers from when Disney had acquired the rights from Saban Entertainment. UPN aired the show until late August 2003, when they severed their ties to Disney. As with previous "seasons", the English version of Frontier featured an original soundtrack and sound effects, character name changes, and content edits pertaining to scenes deemed too inappropriate for young audiences. The theme song of the English version was produced by Chris Horvath. In addition to the theme song, the show also featured music by Deddy Tzur and Inon Zur.
New Video Group released a complete DVD box set of the English-language version on September 10, 2013, in the US, and a DVD collection of the complete English run of Digimon: Digital Monsters, bundling Frontier with the previous three anime series, on October 22, 2013. Manga Entertainment released the series in the United Kingdom on October 29, 2018.
A film companion, ' was produced with the same writer, composer and character designer from the TV show, but was directed by Takahiro Imamura. The film premiered at Toei's Summer Anime Fair on July 20, 2002, along with three other productions. Although the fair was deemed a box office failure, earning 800 million yen (US$6.8m)âÂÂwhereas last edition earned 2 billion yenâÂÂ, the film alone grossed half of it, 460 million yen. The film aired on Jetix in the United States on November 27, 2005, and reruns were broadcast on Toon Disney in 2007.
A drama CD titled was released on April 23, 2003, and is centered on each of the Legendary Warriors sending messages to each other. The cast from the television series reprised their roles.