Liners: Human Species (人間種 [Liner], Ningenshu?) are the primary human race living in the Land of Steel. Ether Liners: Knights (騎士 [Ether Liner], Kishi?, Knights) are a special subset further affected by the harsh envoirnment of the Land of Steel.
Humanity created the A-Ray to help survive in the dying world being filled with Grain. After the death of the planet, the A-Ray and humans went to war. Humans fought to survive, while the A-Ray fought to rule. Humans were on the verge of defeat under the A-Ray lead by the Six Sisters, but the Liners and Ether Liners were created towards the end of the war. This act further killed the dead planet. The war ended with no victor due to the arrival of the Ultimate Ones that appeared to wipe out both sides. The platform of the humans was broken completely by the attack, so they entered a ceasefire with the A-Ray. The grouped together as humanity until the defeat of the outside threat.
Liners are the evolved form of the old humans created to adapt to the Land of Steel without changing their form. Compared to the old humans who cannot live outside without the support of machinery or medicine, they adapted to live in the environment with Grain. The regular Liners do not carry any abilities greater than a normal human. They seek to build a country to reconstruct the old civilization. They are technically considered one of the one hundred A-Ray species.
All the Liners born into the world are affected by the Grain, and some receive an even stronger effect from the environment of the Land of Steel. Babies born with a large amount of Grain within them shape the grain as if the grain is bone, and it emerges outside their body upon adulthood as a Knight Arm: Demonic Swords (魔剣 [knight arms], Maken?). The Knight Arms, being created from the unanalyzed Grain, are able to cause various effects with power strong enough to be considered a weapon. Few Liners shape Knight Arms, and those with a Knight Arm powerful enough to fight in the war are considered Ether Liners. Each Ether Liner only has a Single Knight Arm. The Knights are an aggressive species that can fight the powerful A-Ray without any support of the weapons of the old world. There are currently seventy-eight enlisted Knights.
 Notes - The Great War [Babel's Tale]
After the death of the planet, there was a war between the survived human race and the Hundred A-rays.
Mankind in order to survive, and the A-rays to rule the world.
Under the Six-Sisters who united the unmassed A-rays, the human race were on the verge of defeat. Near the end of the war, mankind created the Knights and the Human Species, and it further killed the planet that's already dead.
There was no victor to this war. It was interrupted by an intruder that suddenly appeared and nearly wiped out both sides.
 Notes - Aristoteles [•••••••• ONE]
8 Life forms that appeared near the end of the war. Unknown existences.
Not only their appearance, but each of their biology differs significantly.
The reason they used this name is a mystery, but the origin is probably a scientist from the old age.
Considering mankind and A-ray as their enemies, they repetitively attacked them indiscriminately. Mankind were broken their platform completely, and the hundred A-rays decreased in number significantly by them.
After the Great War was over, they slowed down their activity by the sea of clouds that covered the sky, but they still continue to slaughter the living things on the planet.
Since then, the human species and the A-rays ceased fire, and till they destroy the common enemy, they grouped themselves together as the human race.
 Notes - Human Species [liner]
Human race on the Land of Steel. Evolved form of the old human beings who adapted to this world without changing their shape. They technically belong to the A-rays as well.
They were able to adapt and live on today's environment, but they still don't carry any ability more than a normal human being.
They are building a country in order to reconstruct their old civilization. Cease-fire with the Hundred A-rays.
- ↑ 4.0 4.1
 Notes - Knights [Ether Liner]
Life form that received an even stronger effect from the drastic environment. They wield a special weapon called the Demonic Swords. Aggressive species that can fight the A-rays equally without any support of firearms of the old age. There are currently 78 Knights enlisted.
 Notes - Demonic Sword [knight arms]
The name of the weapon that Knights carry.
All human species born in this world are effected by Gin. Babies born with a large amount of Gin in them shape it as if it's their bones during their lives, and when they reach adulthood, it is laid outside their body. Because it is created with the unanalyzed entity Gin, it is able to cause various effects and its power is strong enough to be considered a weapon.
Only few humans can shape the Demonic Swords, and those who carry a Demonic Sword powerful enough to be used for war are considered as Knights. Only one Demonic Sword exists per Knight.