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The Blues are a race of insectoid mutant creatures that have replaced mankind as Earth's dominant species in the anime series Blue Gender. Born from the emergence of a mutant gene known as the B-Cell, the Blue are supposedly the instruments of the grand will of Earth itself, created for the sole purpose of purging humanity.


In the early 21st century, human scientists discovered a dormant but abnormal genetic strand which had emerged in various animal specimens. Experimentation on this B-Cell accelerated its growth, transforming the animals that possessed the cell into the first Blue. The Blue grew rapidly, both in physical size and in aggression, leading to a global infestation that left civilizations devastated.

The Blue multiplied at an exponential rate, killing large quantities of humans and converting whole cities into their nests. Their abnormal metabolism meant that they could consume both organic and inorganic matter and their adaptive physiology allowed them to evolve a multitude of different forms, becoming even stronger as mankind fought against them. Due to their ability to evolve and adapt, Blues became increasingly more difficult to kill and the human-Blue war often led humans back to square one.

Within a few years following the Blue's emergence, humanity was on the verge of extinction. Nowhere on Earth was safe and so the remnants of the Earth's political bodies banded together to ensure the survival of the human race, leading many of their people into space. A space station had been constructed in orbit known as Second Earth which soon became mankind's last shelter from the Blue onslaught: only the most brilliant-minded and most physically fit humans made it to Second Earth. As the Blue population continued to swell planet side, those residing on Second Earth made preparations to take back the planet.

In the late 2030's, in accordance with the will of the Earth itself, the Blue died out in a mass extinction event. Since the planet's human population had been drastically reduced (less than 1%) and its survivors were now living a more simplistic way of life without polluting environment or harmful technologies, the Earth saw that the Blue had fulfilled their purpose and with their population overwhelming the planet the next natural step for them was to die off.

But there was still one last duel to be fought.

Yuji Kaido, a hero of the anime and who possess B-Cells in his body, decides to return to Earth to once and find out what Earth's will is. After learning about a new migration pattern of the Blue (which turned out to be part of Blues' mass extinction event), Yuji and Marlene Angel, the heroine of the anime and Yuji's lover, take a group of volunteers (all possessors of B-Cells known as Sleeper Brigade Team trained to fight Blues) and head to an area where a massive nest is located. There they find a group of humans surviving in the area living very simple lives free from sophistication of technologies and from urban pollution. The nest seems impenetrable at first, but the team eventually find an entrance with the help of the local survivors.

The entrance leads to a tunnel where the walls, ceiling, and floor of the cavern are composed with masses of fossilized Blues. Marlene deduced that the Blue had fulfilled their purpose and with their population now overwhelming the planet the next natural step for them was to die off en masse. The human-Blue war ended in humanity as the last species standing. But the joy was cut short as the team comes upon a crystal formation in a massive cavern. A huge, brand-new type Blue is birthed from the illuminating gel-like crystal sitting atop the formation, and kills everyone except for Yuji and Marlene. Yuji kills it after a vicious battle and comes to the conclusion that the giant crystal will hold the answers he seeks. He sends Marlene, who is pregnant with their child, away to the surface to wait for him. He then gets a vision and can see what the Earth itself can see. Yuji comes to understand how mankind can live alongside the B-cells, and returns to Marlene.

All around the world from former Blue Nests, long strings of coalescing energy ascend into Earth's atmosphere and form a ring. Marlene and Yuji watch this, realizing Earth is now a safe place to be, and look forward to the rest of their lives together as the sun sets. A final view of the Earth from space is shown with a slightly garbled narration, presumably by the Earth, stating, "Welcome to your next journey".

Behaviors and Characteristics

The Blue are easily misconceived as being mindless, destructive monsters, but are really acting on the will of the planet Earth itself. They were born for the sole purpose of cleansing Earth of humans which the Earth saw as an infection, thus introduced the Blue as the cure for that infection.

All Blue appear as gigantic insects and they possess the behavioural characteristics of such. They make their nests in former human population centres, building vast hives from buildings networked together by producing new structures and tunnels from the materials they consume. When hunting, they preserve the bodies of their prey by wrapping them in tight cocoons of mucous for subsequent consumption.

Blue are highly adaptable. Over the course of the Blue Armageddon, humanity would implement new weapons and strategies to combat the creatures. With each new threat they faced, the Blue would evolve into a new form to frustrate the humans' efforts.

Humanoid Blues

There are, Blues that possess human appearance. They act, speak, and articulate like any normal human beings. But if they are exposed to prolonged environment of intense stress, abnormalities of B-Cells within them begins to reveal themselves and they awaken as new-type Blues. This Blue type is even more threatening because they can resemble and behave as if they are humans and therefore are less conspicuous and can avoid suspicion, all the while carry out the mission of Blue. Once B-Cells awaken within them, they may look humans, but their dispositions are no different from that of Blues. At that stage the humanoid Blues can interact and blend into other Blue species.

The display of aggression may vary depending on individuals. And until B-Cells in their bodies are fully awakened, these new Blues are subject to attacks just like normal humans by their more monstrous cousins.


  • Almost all Blue variants have a common organ known as a 'core'. It appears as a tube of flesh with a round orifice which is usually exposed. It is unknown what the core's biological purpose is, but destroying a Blue's core will result in the creature's immediate death. However, as the series progresses Blues evolve to the point where they can shield cores with their appendages or embed cores within more durable parts of bodies. The Blue that fought against Yuji in the last episode did NOT have core at all.
  • Blues (with the exception of humanoid Blues) cannot swim: if they fall into deep enough water they will drown.