Finally what you’re getting has been revealed.

As first mentioned here, in Asian stores outside of Japan, if you buy 3 boxes of the new booster “Code of the Duelist” (not a Card of the Day, as we keep informing everyone.), you can get a coupon that you can turn in at a later point for a Storage case.

The storage case is a green Storage Case featuring Firewall Dragon, Yusaku’s ace monster:

Source