|Voice Actor||Hirata Hiroaki (平田 広明)|
|Paul St. Peter|
Leomon is the first opponent of Deserted Island's Battle Arena. When the player meets him, he considers his mission to be destroying the Chosen Children. He uses the Gears of Battle deck, a Green/Nature and Black/Darkness deck with 3 attack, defense and evolution speed. Upon being defeated, he praises the player, and realizes that he should just focus on enjoying the game, asking the player for his help on that.
In-game, Leomon is shown with blank eyes, as he looked under Devimon's brainwashing.
Leomon first appears in Episode 10, "The Messenger of Darkness, Devimon!", where he sees a Black Gear flying while on Infinity Mountain. He's then attacked by Orgemon. Leomon, however, refuses to fight him as the Black Gears are more important, though Orgemon does not care and attacks him with his Haouken, which Leomon answers to with his own Jūouken. Their fight is then interrupted by Devimon, who tells them that the Chosen Children have arrived. This prompts Leomon to attack him, though it accomplishes nothing, and Devimon returns the favour with his Death Claw, which brainwashes Leomon.
Leomon then attacked the Chosen Children as they went down the mountain due to his brainwashing, despite Gabumon and Patamon acknowledging him as a Digimon of justice. The Chosen Children tried to run away, but Orgemon blocked their escape route. Unlike Leomon, Patamon and Gomamon knew Orgemon was an evil Digimon.
Leomon is the eighth obligatory boss of the game, fighting Greymon, Kabuterimon and Togemon at the end of Episode 10, "The Messenger of Darkness, Devimon!". For the battle, all three will start in their Adult forms and remain in them for no SP cost. Leomon can counter attacks automatically at random, and deal damage to one party Digimon with Jūouken and the entire party with Shishiou-maru. Upon being defeated, he drops the Counter DigiPiece that allows the player Digimon to counter attacks as well.
After the Chosen Children defeated Leomon and Orgemon, Devimon appeared and caused a landslide, separating both groups.
Devimon, Leomon and Orgemon reappear in Episode 11, "The Mysterious Mansion", where the former is the one responsible for the namesake mansion, a trap for the Chosen Children. After Yagami Taichi and Agumon escaped from Orgemon, who found them in the toilet, Leomon attempted to block their escape. After Devimon broke File Island into pieces, Leomon appeared once again and tried to attack Taichi, but a light came out of Taichi's Digivice, which broke Leomon out of Devimon's brainwashing. Leomon then attacked Devimon once again with a Jūouken, and told Taichi to run away as the Chosen Children had been summoned to the Digital World as their only hope, before shooting yet another Jūouken which sent Taichi and Agumon away. Leomon was then brainwashed once again, and Devimon, now accompanied by both Leomon and Orgemon, merely decided to kill the Chosen Children slowly, one by one.
Leomon reappeared in Episode 15, "Centalmon, the Guardian!", inside the ruins after Centalmon explained the Digivices to Izumi Koshiro and Tachikawa Mimi. Centalmon himself was surprised at his appearance, but quickly realized that he was being controlled, just like Centalmon himself had been only shortly before. Koshiro, who understood Centalmon's words, used both of their Digivices on Leomon, as they "bring light to the world and drive out the darkness". Leomon then ran away.
After the Botamon Takaishi Takeru hatched evolved into Koromon in Episode 17, "Adventure! Patamon and I", Leomon appeared in the Village of Beginnings. Takeru and Patamon then escaped from him and hid, where Takeru wondered what to do and Patamon answered that they had to get the Black Gear's power off of him, though Takeru did not know how. Orgemon then joined Leomon and threatened to hurt the village if Takeru and Patamon didn't come out. Before they could, however, Leomon found them, though he was stopped from hurting them by the arrival of Ishida Yamato and Gabumon. At the same time, Taichi evacuated the baby Digimon. Another Black Gear then entered Leomon, turning his skin grey.
This "Dark" Leomon is the sixteenth obligatory boss of the game, fighting Agumon, Gabumon and Patamon at the end of Episode 17, "Adventure! Patamon and I". Leomon's counter is stronger now, having become a Super Counter. He can still use Jūouken and Shishiou-maru. Upon being defeated, he drops the Mega Heal+ DigiPiece, which allows the equipped Digimon to use the technique of the same name to heal 800 HP of all allied Digimon.
Though the Chosen Children were able to defeat Leomon, they could not get the Black Gears out of him. However, Izumi Koshiro and Tachikawa Mimi arrived soon after, and explained how the Digivice could drive out the darkness. Taichi and Yamato followed said instructions, and Leomon went back to normal. Realizing he had no chance alone, Orgemon then escaped.
Leomon then told the Chosen Children of rumours about darkness covering the Digital World, and how Chosen Children from another world would come to save it. While Taichi realized it referred to them, Yamato pointed out he had no proof of it, so Leomon added the Chosen Children had the power to evolve their Digimon. Koshiro then realized that it meant that, if they extinguished the power of darkness, they would be able to return to their world as they would be unneeded in the Digital World. As such, they had to defeat Devimon, who stood at the center of the power of darkness. The Chosen Children and Leomon then steeled their resolve, and decided to do just that.
The group at the base of Infinity Mountain in Episode 18, "Angemon's Awakening!", where they were soon joined by Takenouchi Sora and Kido Jo. Leomon then joins the party, taking the third slot. As a party member, Leomon can still use Jūouken and Shishiou-maru, still counters upon being hit though with the normal Counter, has 2000 HP and no SP, and can't gain EXP, level up, or be manually controlled.
Leomon joins the Chosen Children in their first fight against Devimon. Despite being defeated, Devimon was unhurt from said battle, and Taichi realizes he was just toying with them. Afterwards, the powers of darkness expanded, and Devimon defeated everyone except Takeru and Patamon, with Taichi being the only one of the rest to stand back up after Devimon's attack. Devimon then decided to kill Takeru, as with him gone, he'd have nothing to be scared of anymore. However, Leomon blocked Devimon's attack with his body. While Leomon survived, he could not help in battle any longer. As such, he's not part of the party for the second fight against Devimon.
After Devimon was defeated and Orgemon reappeared, Leomon asked him if he still wanted to fight, but Orgemon just ran away. He also accompanied the Chosen Children as they talked to Gennai.
Leomon, Mojyamon, Yukidarumon, Meramon, Elecmon and Centalmon offered to help the Chosen Children reach Server Continent in Episode 19, "Departure - to a New Continent!". After meeting Leomon deeper into the forest, he warns the Chosen Children that trees were falling in the direction of the place they were in due to Leomon cutting them down for wood for the raft. Taichi then asked if they could take some to make a bridge for Centalmon, which Leomon agreed to. After the raft was completed, Leomon carried it to the ocean, and encouraged the Chosen Children by telling them that if anyone could do the trip, it was them. He then said his farewells to them as they sailed into the Net Ocean.