The Archive (or Archiver) is the God of Infinity Fortress.
In Volume 9 of Getbackers, Kazuki first mentioned there being a God above the Infinity Fortress, and that Makubex was trying to make a deal with this God to pass final judgment. Kazuki explained that God was more powerful than those below him.
As the series advances, we eventually learn of the God of the Infinity Fortress - The Archive.
The Archive is a sentient "self-evolving" system containing all possibilities, all objects, and chaos. It was a massive electronic repository with all timelines within it. Kagami placed this in the adjacent dimension using the magic mirror effect, thus causing this mere program, to become actuality. Because the Archive is a self-evolving system, it ascended to the point that even its creators could do nothing to stop it; only implement one last program within it. The King of Creation.
The Infinity Fortress is the unification of all qualia (metaphsyics) in the universe. Qualia is "the way things seem" to us. Meaning that it is all minds; all truths. While one world is real, another world is equally real. Volume 38 shows Ginji and the others looking outside of the Infinity Fortress, and its a desert. Makubex's dream has come true, and the others see the same thing; that the world has fallen into ruin. Madoka seen, within the city of Shinjuku(which shows that there is more than one world outside of the Infinity Fortress). Natsume, and Semimaru are later seen at Paul's coffee shop. Semimaru knows that their reality is about to be erased. Remember, that at the start of the arc, Ban and Ginji walked into the Infinity Fortress, not knowing that they had walked into a different timeline. This means, that the Infinity Fortress is in fact, all worlds. Because remember, the Infinity Fortress connects to all space-times. If it goes offline, everything else does, as Der Kaiser tried to prove. The Archive is the mind behind the Infinity Fortress, and the Infinity Fortress is a place where all truths can exist, where all worlds can exist. If it seems a certain way, it exists, even if it all seems like a dream. At the same time, the Archive encompasses all of it.