The Galaxy Buster is a superweapon that can destroy an entire galaxy. It launches several Star Busters to all surrounding stars of the Galactic Core causing those stars to supernova and turn into black holes. These black holes gravitationally fight the Galactic Core causing them to combine into a large black hole. The extreme gravitational fields also causes more giant stars to supernova, causing a chain reaction that creates an enormous black hole that swallows the galaxy. After that, the enormous black holes shrinks down to the size of a pinhead, and then explodes sending a shockwave throughout the Intergalactic Void. Nearby stars in other galaxies 2 million lightyears from the target galaxy get destroyed from this aftershock.
The Galaxy Buster was first developed 5 million years ago by the Chch'ptk, an ancient race that is said to be the one of two races capable of intergalactic travel. Their plan was to quickly eliminate the Kklxin, a hostile alien race in a neighboring galaxy, who had also developed a Galaxy Buster for themselves. The original names of the two galaxies these races are from are unknown, so the galaxies are named after the respective race. The two aliens races engaged in a power struggle and eventually destroyed each other by launching the Galaxy Buster at their two galaxies. Both races were on the brink of extinction. Their numbers were reduced from several trillion to no more than 100.
The two of them realized that their hostilities would cause unwanted destruction, so the survivors travelled on motherships, making use of whatever resources remained after this cataclysmic event. The two races set off in opposite directions so that they would never meet again, the Kklxin heading for the nearby Milky Way galaxy.
The whereabouts of the Chch'ptk are largely unknown, but the Kklxin have established themselves an empire in the Milky Way galaxy. Their last copy of the Galaxy Buster was stolen by the Harbingers in an attempt to destroy all other sentient life in the galaxy, but their plans were foiled by the EIT and DFM. No Galaxy Buster has been seen or heard of ever since.