Black Point (ブラックポイント Burakku Pointo) is the gateway that connect the Present World with the futures.
Z/X Encyclopedia Entry
Gateways to alternate realities that suddenly appeared in five locations across the world.
These nightmarish gates constantly pour out the Z/X without end, ushering in an era of destruction and genocide. They are jet-black because they are zones that completely consume all surrounding light, causing them to be called "Black Points". These dome shaped black barriers make the area impenetrable, it's impossible to let people know they're being invaded or not, and it's impossible know or hear what's going on inside. Since the affected area (in the dozens of kilometers) is infested with Z/X, all public access is forbidden.
The first Black Points appeared at the following points:
Washington D.C. (United States of America)
Buenos Aires (Argentina)
Pretoria (South Africa)
Shortly after the appearance of these 5 gigantic Black Points, 4 other Black Points formed in Japan one after another, though they were smaller than the first. Japan, facing 5 Black Points consuming huge amounts of area on such a small land, was badly bruised, and to make matters worse, it lost its capital. The Black Point that formed in Tokyo spans more than 50 km in diameter.