Digimon Adventure V-Tamer 01

Digimon Adventure V-Tamer 01 (デジモンアドベンチャーVテイマー01) was the first and longest-running Digimon, printed in the pages of magazine. Starting on November 21, 1998, it ran to fifty-eight chapters and ended on August 21, 2003. This manga introduces the character of Taichi Yagami, an alternate Taichi to the one that features in the Digimon Adventure TV series.

Plot
In this universe, Taichi is involved in a V-Pet tournament, where he is told he cannot play because the Digimon in his V-Pet isn't recognized as being a real Digimon. However, after the tournament is over, Taichi plays the winner of the tournament, a boy named Neo Saiba, and their battle ends in a tie—something that is supposed to be impossible. Later, Taichi is summoned to the Digital World by a digimon called Lord, and there he meets the mysterious Digimon in his V-Pet, Zeromaru the Veedramon. Taichi and Zeromaru travel to Lord MagnaAngemon's castle with the aid of Gabo the Gabumon, and there Lord MagnaAngemon begs Taichi to find the five Tamer Tags and defeat the evil Daemon, who has disrupted the peace of the Digital World.

Along the way, more humans are brought to the Digital World by Demon, including Neo Saiba, Rei Saiba, Sigma, Mari Goutokuji, and Hideto Fujimoto. Neo is chosen to raise the Digimon that will hatch from the Super Ultimate egg Demon is raising. Rei Saiba, Neo's sister, has a Digimental that will allow the Demon's experimental Digimon to evolve to a level beyond Ultimate. The others, called the Alias III, are to help Neo and Demon with their Digimon. Hideto's Partner is Omegamon, formed by the Jogress of Warg and Melga, a WarGreymon and MetalGarurumon respectively. Mari's Partner is a Rosemon and Sigma's is a Piedmon. They are all villains that eventually reform except Rei, who has no Digimon Partner or evil intentions.