Now destroyed, the DVA, or the Dimensional Variance Accelerator, was the brainchild of SEBEC and the particular efforts of former CEO Takahisa Kandori along with the researchers Setsuko Sonomura and Dr. Nikolai, the latter two of whom still work with SEBEC. Their goal was to create a weapon; in a sense, they may have succeeded.
In the strictest of terms, what the prototype and only extant model of the DVA did was create a pocket dimension, carved out of the folds of reality. This reality was shaped and directed by the mind of the individual within the machine--for that was the secret of the system. A human needed to be present within the machine for it to function, and not just any sort of human would do. Only certain people were compatible with the DVA. Of course, a machine of such great power did inflict certain stresses upon the psyche. Some people... broke, compatible or not.
Experiments on the first-isolated compatible subject, Maki Sonomura, eventually resulted in the creation of Mikage-cho, a world which continues to linger on even without the DVA's direct influence. Later, the machine fell into the hands of Kandori himself, who attempted to use it to become a god, only to meet his end at the hands of those who defied him. It passed from his possession to others, until the overtaxation of the machine by Masahiko Irie and Mikiya Ryouhara in the creation of the pocket dimension Maboroshi broke it, rendering it inert and nonfunctional.