Z/X Zillions of Enemy
The story of Z/X is set in a future not so far from now. Gates to the five different parallel worlds suddenly appeared in the world, and inhabitants of those worlds (later known as "Z/X", an abbreviation of "Zillions of enemy X") start pouring from those gates to invade this world. The five parallel worlds are the different shape of the earth in future, and they fight against each others in the present in order to ensure the survival of their own future. Later, humanity received help in the form of a card-shaped device that able to capture and enslaved the Z/X. By using this device, humanity begin to fight for either their own or the five parallel worlds' future.