Digimon Conquest is a made up digimon game consisting of a Nintendo DS game, card game, and online game that requires cards. It is constantly reffered to in Fan: Digimon X-Fighters.
The online game requires at least one character card and you can use some cards to modify your digimon, similar to Digimon Tamers computer game that Henry plays beofre meeting Terriermon.
The Nintendo DS game asks a series of questions to decide your starter digimon.
The card game seems to work the same way as the online game.