In the future not so far from now.
Gates to the 5 different parallel worlds, "Black Point", suddenly appeared in the world—
Immediately after that, fantastic creatures that visited from the other side of the gates start to invade.
Those fantastic creatures are the inhabitant of the five worlds on the other side of each gates.
And the five worlds are the future shape of the earth in different time axis.

Their goal of invasion is only one.

In order to ensure the survival of their own waning future because it was divided into the 5 futures,
they have to suppress the future of the other parallel worlds, in dimension that becomes the singularity point.
Without any choice, humanity were involved in the conflict of the parallel worlds inhabitants that surpassed human knowledge.

The only thing left to overturn the desperate situation, is a card-type device.
As for the humanity who obtained the means of counterattack,
some people naturally use it in order to realize their ambitions,
some people use it in order to survive,
some people use it in order to protect something precious to them,
they all jumped into the circle of battle with the device in their hand.

Eventually, humanity comes to call those fantastic creatures
Zillions of enemy X
or "Z/X"—————

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