Originally thought to be an inscrutable alien race, the Hideauze are a species of genetically enhanced space-faring life forms, distantly descended from human beings before the fifth ice age. They are currently engaged in a perpetual war of extermination with The Galactic Alliance of Humankind.
The Hideauze are mollusk-like lifeforms that have been at war with humanity since the beginning of recorded history; they possess the ability to evolve their bodies at a staggering rate and develop devastating bio-weapon systems that rival, and in some cases exceed, the capabilities of the Galactic Alliance of Humankind. However, according to Chamber, the unique characteristics of the lifeforms found on Earth have the exact genetic makeup as the ones in space, with the exception of their outer exoskeletons, which have been adapted for underwater life. Earth's Hideauze take on the form of a smaller, squid-like species. Their behavior is rather docile, but very dangerous when provoked. On Earth they are referred to as Whale-squids. Spacefaring Hideauze are able to live near a star without ill effects.
The Hideauze are first seen during GAH Closer pass operation. Their nest is protected by a power weapon known as the "Blossom Sail" and the intense stellar radiation of the nearby star. The GAH is initially successful in destroying the weapon but it is able to regenerate before the GAH has time to destroy it again.The Whale-squid (or Earth Hideauze) was said to be a sacred creature that was not to be disturbed, as suggested by the crew alongside Ridget. According to the rumors in Gargantia, the citizens became worried that if the Whale-Squid were to be attacked, a bad omen will fall upon them. According to Chamber, over time, the "survival" was suggested to differ greatly than the Alliance's interpretations. The humans on Earth living alongside the Whale-Squid was noted to be "co-existence."
On the other hand, the space Hideauze are very virulent and dangerous. The Alliance has been fighting the Hideauze for centuries in their war, only to subjugate them to ensure human survival. Thus, suggesting that the humans in space have been fighting the Hideauze continuously, advancing their technology to combat the Hideauze.
Due to the fact that the Whale-Squids are far more powerful than the Diver Yunboros, any areas that they inhabit are generally avoided. This brings conflict within the connected ships of the Gargantia Fleet as the Whale-Squid nests are located on top of very lucrative areas of salvage and Lost Technology. As a result, several ships have opted to separate from the main fleet in order to procure these underwater treasures, with the intention of enlisting Ledo and Chamber to fight off any Whale-Squids that interfere. Unfortunately, these separations would greatly reduce the Gargantia's defensive capabilities against pirates or other dangers.
When Ledo finds lost human data files, he discovers that the Hideauze were created by a genetic-manipulation program put into effect by a group of humans trying to escape the new Ice Age. Known as the Evolvers, these scientists genetically changed humans into higher lifeforms, able to adapt to zero-pressure and atmospheric conditions. The Continental Union, the government of Earth, opposed these human experiments and attempted to destroy the Evolvers, leading to a war between the Evolvers and the C.U. It is thought that the Continental Union became the Galactic Human Alliance and that the Evolvers became the Hideauze. As Chamber said, they "devolved" due to playing with their genetics. Specifically, due to their genetically engineered rapid adaptability factor, the Earth Hideauze rapidly devolved to a simpler form, in the absence of threats from natural selection.
From videos seen in the lost human data files, as well as observations made on Earth, it appears that normal humans and the Whale-Squids are capable of coexisting without violence, when certain conditions are in place.