On the 15th of May you can enter the "Lab" on the Map. Within there you will find the Rental Counter and the Password Machine.

You can enter the 8 Digit card code to unlock the card at the Rent Counter and you can add it to your deck. Whenever you win a duel with a rented card you will have to pay a DP fee and you can only rent up to 3 cards max.

Here is how you can avoid the 3 card cap and the DP fee:

• Enter 8 Digit code on the Password Machine for the cards you want to rent (only needed once for every card, you can rent them up to three times, unless they are limited or semi-limited)

• Talk to the Rental Counter Guy

• Choose your three cards you want to rent and hit X, they will now be shown in the "rental" tab

• Back out of the Rental Counter Menu

• Open up your PDA and go to the Deck Menu

• Switch to the rental tab and add the 3 rented cards to your deck

• Back out of the Deck Menu and enter the Rental Counter Menu again

• Switch to the rental tab and hit Triangle -> Selected Card Menu -> Empty Card Selection Tab

You can repeat this as often as you want, but you can do this only with 3 cards at a time.

As soon as you remove the "stolen" cards from your deck to put them back in the trunk, they will be removed entirely since they technically don't exist.