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 six children (Takuya, Koji, Zoe, Tommy, J.P. and Koichi) 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.