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".

A one-shot pilot manga, made in Summer 1997, involving battles between more-or-less holographic Digimon. However, this manga was published as a special in volume two of Digimon Adventure V-Tamer 01, where an omake page by the author explained that the hero of this manga, Kentarou Kamon, was the source and inspiration for the design and character of Taichi Yagami, the protagonist of V-Tamer 01.

Special one-shot between Digimon Adventure V-Tamer 01 and Digimon Adventure (2020).

Seven kids are transported to the Digital World, a strange place where digital creatures called "Digimon" reside. A group of Digimon soon befriend them and keep the kids out of harm's way. The children then discover they are the Chosen Children, which protect the Digital World from evil Digimon like Devimon and Vamdemon.

Seven kids at summer camp are unexpectedly transported by 'digi-vices' to a colorful and enigmatic world. Lost and alone, they are befriended by small digital monsters, Digimons. The kids and their Digimon partners quickly become inseparable, and the strange creatures guide their human friends through the wondrous DigiWorld, protecting them from the hordes of evil Digimons. The group soon discovers that some of the giant Digimons they encounter are not evil Digimons but good Digimons gone bad. A dark power is corrupting even the most gentle of Digimons by embedding Black Gears into them, turning them into vicious monsters. Creating chaos and destruction wherever it goes, the evil power threatens all of DigiWorld. 
As they try to find their way back home, the seven kids are drawn further and further into the mystery. Through teamwork and trust, they help their newfound Digimon friends digivolve from 'monsters in training' to giant champions that must save the DigiWorld from the powerful evil intent on destroying it. 
(Source: Tokyopop)

Digimon Chronicle was the storyline accompanying the 2004 Digimon product line. Originally rumored to be a new, full-blown manga to replace V-Tamer 01, it eventually transpired to be mostly prose text, printed in the booklets which accompanied the "Pendulum X" digital pets. These booklets also contained short, non-sequitur six-page manga. There are four "chapters", one sold with the Pendulum X 1.0, another with the Pendulum X 1.5, another with the Pendulum X 2.0, and the final chapter with the Pendulum X 3.0. 
This fiction tells the story of a Digital World controlled by a scientist computer named Yggdrasil. Because Digimon had multiplied so much in the past, Yggdrasil, the host computer, was unable to handle the load and the Digital Hazard occurred. Yggdrasil then created the "New Digital World", consisting of three layers for the past, present, and future - Urd, Versandi, and Skuld, respectively, and then let loose with Project Ark and the X Program to eliminate any Digimon Yggdrasil no longer wanted. However, the Digimon adapted by obtaining a program called the X-Antibody, which strengthened them, changed their form, and made them immune to the X Program. Yggdrasil sent in the Royal Knights, thirteen Digimon devoted to keeping order in the Digital World, and at this point Kouta, Yuuji, and Shinji, three humans, somehow found their way into the Digital World and met their partner Digimon, Dorumon for Kouta and Ryuudamon for Yuuji. Kouta and Yuuji resisted Yggdrasil and the Royal Knights, but Shinji apparently sided with Yggdrasil. 
Source: mangaupdates

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