The blue card of China Merchants Bank Doraemon Credit Card is equivalent to the main card in the set of cards, and the other three cards belong to the auxiliary cards in the set of cards. No matter which secondary card you apply for, the blue primary card is approved at the same time. The secondary card has received the production cost, and there is no annual fee regardless of whether it is swiped. However, the big blue card must be swiped six times a year to avoid its annual fee.