No official name has yet been revealed. These are the aliens that arrived during the event known as catastrophe.
The aliens are humanoid with pointed ears and four eyes, and are giants. They act remarkably human. Some see humans as pets or creatures to feed like you would pigeons, others just want to kill them for fun while some eat them as a delicacy.
The main forces used aircraft, gigantic orbital dropped mech, as well as guys on the ground and hound creatures for the initial extermination. It is hinted that the alien has gathered extensive information about human as they have access to most (if not all) language of human.
After the first attack was completed, and most humans dead, they allowed civilians to go out with their children, and hunt remaining humans for sport. They use decoys that look like humans from a distance that walk around repeating the same phrase, to lure humans over to it. Their operation include "harvesting" human by force (or persuasion) into a cage shuttle where the human is transported to the "processing center".
The aliens also broadcast messages of peace, claiming the war was over, trying to trick remaining humans to stop fighting and come out of hiding so they can kill them as well.
The aliens have a zoo containing creatures from many different worlds, which apparently they have already been to and eliminated.
The alien's main ship has their entire world within it, being far larger on the inside than it is on the outside. A thriving city is shown. Some part of the ship is believed to be infected by creatures they failed to tame and isolated. The alien used some of these area for a alien Colosseum where aliens from different world is pitted to fight each other in a deathmatch. Kato and friends were forced to transferred here while on a mission to liberate as much human from alien.