Careful Scouting
If this were occurring on a planet like Earth, it would be no different from the end times. In fact, given the scale of the current conflict, it showed the sturdiness and superiority of this world that only a 100-kilometer area was troubled by this, not to mention that the ground had never cracked nor shattered, only space.
The good news for Dante was that even though his energy was being consumed crazily to maintain the constant firepower, he could sense that the space that had been cracked was repairing itself, and this monster would be forced back soon.
In fact, it was only through his own ignorance that this monster even had a chance to enter real space. Sub-space was an empty void in the normal universe filled with nothingness, and space mages sometimes even used it as a garbage can to dump stuff.