Red Card

The Red Card (レッド・カード) is a special card used in Digimon Tamers.

Digimon Tamers
The Red was created by Shibumi to allow the Tamers to fight inside the D-Reaper without degradation. It works perfectly until the program cancels out the card's effect due to an error in the algorithm causing the biomerged Digimon to revert to their base forms.