Digimon Adventure: V-Tamer 01

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 HolyAngemon, and there he meets the mysterious Digimon in his V-Pet, Zeromaru the Veedramon. (Source: Wikipedia)

*Note: Includes the one-shot "C'mon Digimon: The capering monster BUN"*.