The Digital Card Game was a card game in the Digital World created by a Security Program posing as a Rosemon in order to trap A and cast him deep into the net. The Security Program created a trap triggered by beating A in a card game. When A lost a fight, he would be forced into the Security Program's directory where his hacking abilities would prove useless.
However, knowing A could not be confronted by her directly she decided to hunt down a Card Tamer that showed potential, taking on the form of a Rosemon to fool A and keep a low profile to prevent A from finding out what she was up to. The card game takes place in the Digital World from Digimon Adventure