The basic premise of the Cardfight Vanguard trading card game, as explained in the anime, is that the two players represent astral spirits dueling on the fictional planet Cray. The cards in players’ decks, called “Units”, represent characters from Cray that players can “Call” to the field to fight for them. Players alternate turns calling, attacking, and defending with units. When one player reaches six damage, or there are no more cards in his or her deck, that player loses the game.
Each unit has a Name, Clan, Power Level, Critical Value, and “Grade”, which ranges from 0 to 4. Grades 0 to 2 have a shield value, and most units have one ore more skill, with exceptions. Overall strength of units increases with grade, but a unit can only be called if the player’s vanguard is of that grade or higher. A deck must contain exactly fifty cards, including exactly sixteen “Trigger Units.” There can be no more than four copies of the same card, no more than four total Heal Triggers, and no more than four cards with the keyword Sentinel (守護者 Senchineru?) in a deck. There is otherwise no restriction on how many cards of a certain clan or grade must be used. There may also be an extra eight cards, but they all have to be G-units, and they do not count in your deck. They are placed in a separate place called the Generation Zone located above the damage.