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Gauna (奇居子) are an alien lifeform which are composed of a True Body and a Placenta. They have the ability to shapeshift and take many forms. A Gauna cannot be destroyed unless its True Body is pierced by a Kabizashi, otherwise it will continuously regenerate. Gauna consist of two primary materials: A Gauna's Placenta, or exterior covering, and its True Body. The Placenta appears to be highly malleable, able to move at speed, extend significant distances, morph into different forms, and be used for a variety of purposes. Placenta are shown to be able to create many different materials and even complex machinery, including:
  • Human organs
  • Human eyes
  • A functioning human uterus
  • A biological Heigus Cannon
  • A membrane able to deflect a full blast from a Heigus Cannon
  • A complete form of the deceased Hoshijiro
And of course, a Graviton Radiation Emitter, a device which was impossible to build, but through the Placenta's ability to generate anything, was created anyway. Gauna seem to enjoy using their Placenta to mimic human shape. Even before the war with the Gauna began, the first Gauna to descend to Earth had a humanoid shape, even including vague eye and mouth organs. The True Body is shaped a bit like a comma, or a magatama. A thicker, orb-like portion is the "brain," while a spindly tail forms the "spine." A Kabizashi (and later artificial Kabi bullets) must pass through the True Body to cause a rejection of the placental membrane and the foaming of the entire Gauna core. Even stripped entirely of Placenta, a True Body can regenerate completely with enough time.

Prior to the Sidonia's discovery of the Kabizashi and the artificial Kabi, there was no way to destroy a Gauna's True Body. It is unknown whether any other colony ships discovered different ways to combat the Gauna.


The Gauna were discovered some time before 2171 AD, when a Mass Union Ship was detected at the outer edge of the Solar System. With an estimated trillions of Gauna within the Mass Union Ship, humanity lived in uneasy peace for over 200 years.

In 2371, the Gauna Mass Union Ship approached Earth and cast down 46 Gauna to the surface. These Gauna immediately began to kill and absorb humans on the surface. Gauna also began to consume marine life and, we can assume, all other life on Earth, until, at some point, the Earth was split into two. Split into two hemispheres, the Earth was destroyed, with kilometers-thick Gauna placental arms emerging from the Earth's core.

During this time, Humanity was fervently building and sailing seed ships away from the Solar System. Recognizing that there was no way to defeat the Gauna, their focus turned to the continuation of the species. Though hundreds of seed ships were sent out, only two Seed Ships are known by name: Sidonia, and Aposimz.Sidonia left the Solar System on 2 August 2384.

Sometime around 2800 AD, Sidonia discovered an unknown artifact in deep space. When investigating this unknown artifact, the crew members of the Sidonia discovered the only substance known to pierce a Gauna's True Body: The Kabizashi.

The last major incident of Gauna activity prior to the main storyline was 100 years prior, when Gauna were encountered and a Gauna wiped out 99% of Sidonia's population.

Gauna Biology Edit

Gauna seem not to have organs as humans know them. Instead of an interior made up of distinct organs, their body appears to be split into only two substances. Any organs that may exist inside the True Body are conjecture, since nothing can penetrate a True Body except a Kabizashi, and Kabizashi cause immediate foaming of the True Body.

Gauna appears to have none of the traditional components of bodies: blood, viscera, organs, eyes, lungs, stomach, or other materials. Instead, their Placenta acts as a universal organ. The Placenta is able to take on any form at will, from tentacles to human features and even Heigus Engines. Planar angles seem impossible for the Placenta to maintain for long, and the default shapes all revert to tubular, bulging, and tentacled forms.

Aside from Placenta, Gauna have another substance, called "husk." Husk is derived from the True Body, requiring a Kabizashi or articificial Kabi to penetrate. Using alternating layers of placenta and husk, some Gauna can become incredibly strong, resisting both conventional attacks and kabi attacks. In those cases, a combined arms approach is needed, to strip through each layer in succession. Destroying a layer of husk does not cause foaming of the Gauna.

Gauna original

A Gauna in its natural state

Gauna mimic

A Gauna immediately after devouring a human and his Guardian

Gauna, in their original form, appear to be singular beings outside of Mass Union Ships, and appear to either hide in structures or wait for prey passing by. The first Gauna appearing the main storyline is hiding in a large fragment of ice; the Gauna encountered in the Kabizashi artifact was hiding in a deep crevasse. When encountered alone, they instinctively reach out for and devour what is near them. They exhibit rapid growth and immense size, though there appears to be some practical limit to their size. Most appear to be an order of magnitude larger than a Type 18 Guardian, though some can be much larger. The True Body appears to be slightly larger than a human being, though it can elongate as well.

Gauna anatomy

Gauna anatomy

It is important to note that, no matter how human the Gauna may look, none of their Placenta is essential for survival. Biologically, the only necessary component for a Gauna to survive is their True Body. On many occasions, Guardian pilots will strip the entire Placenta off a Gauna, only to see the Gauna regenerate mere hours later. Even direct hits from Mass Driver Cannons will only cause the Placenta to temporarily detach from the True Body.

Chimera, created from the fusion of Human and Gauna, retains the immense plasticity in their Placenta. Though they look far more human than a normal Gauna, any semblance of organs or physical structure is Placenta mimicking that structure. The Chimera Kanata had several large pieces of debris shoved entirely through its "head," and only suffered momentary discomfort. Benisuzume is stripped of Placenta several times, regenerating both its structure and the fully-formed human body of Hoshijiro each time.

Interestingly, as long as it is severed before True Body destruction, Placenta remains active even after the True Body is destroyed. This means that placental samples, including humans formed from Placenta, remain viable and active without having to be attached to a True Body.

Chimeras Edit

Human eggs and sperm that are combined within a placental human's uterus can form a Chimera. A Chimera is a fusing of human and Gauna DNA, combining the intelligence and communication of a human with the immense power of the Gauna. Chimera can only be grown from female humans regenerated from the Gauna Placenta; given how rare this occurrence is, and how rarely a placental human is found, Chimera are usually once in a lifetime opportunities.

Chimera embryo

A Chimera embryo

In Knights of Sidonia, we know of three Chimera: a Chimera created by Ochiai prior to the story, Tsumugi Shiraui, and Kanata. Of those two, Tsumugi shows a measurable amount of human empathy and concern, including a strong attachment to her human friends. Mentally, both Chimera are infants, though physically they are immensely strong.

Chimera have the appearance of a human, but contain no reliance on human organs or skin. They are completely immune to the vacuum of space, can emit and radiate Higgs Particles, and can travel at immense speed. It is hinted that the True Body of a Chimera lies in the area humans associate with a heart.

Mass Union ShipEdit

A Mass Union Ship (衆合船 Shugafu-sen) is the aggregation of countless Gauna. A single Mass Union Ship can be extremely large in diameter. Most Mass Union ships contain trillions of Gauna, but smaller ones are known to exist. Sidonia encountered a Mass Union Ship containing only 5,000 True Bodies; this Mass Union Ship contained enough Higgs particles to wipe out Sidonia.

During the smaller Mass Union Ship's arrival, it is discovered that, even with a huge size and over 5,000 True Bodies, a Mass Union Ship can disguise itself as gas particles, remaining invisible even to Sidonia's sensors.

Small mass union interior

The small Mass Union Ship's interior


Mass Union Ship

Mass Union Ships seem to be an immense conglomeration of Placenta and True Bodies, leading the Sidonia's crew to believe that they are linked in some way. When annihilating the small Mass Union Ship, Nagate discovers that the True Bodies form into a single body at the interior, hinting at a greater mystery behind its immense size and power. Later in the series, Mass Union Ships appear in number, and contains multiple True Bodies inside of each. As the conflict builds, Gauna are incorporated into their larger form more and more often.


  • The Kanji used for "Gauna" mean strange (奇, ki), living (居, kyo), and child (子, ko)
  • The Gauna from "Sidonia no Kishi" are based on similar beings from Tsutomu Nihei's previous works, specifically from the ones in Abara and Winged Armor Susumega.


Knights of Sidonia Characters
Gardes Pilots

Nagate Tanikaze | Izana Shinatose | Shizuka Hoshijiro | Honoka Sisters | Mochikuni Akai | Hinata Momose | Kashiwade Aoki | Izumo Midorikawa | Eiko Yamano - Toutarou Yamano| Samari Ittan | Tonami | Kouichi Tsuruuchi | Ichirou Seii | Norio Kunato | Kaoru Hazama | Ryouhei Kasuga | Kujira Negi | Hamagata | Hashine | Suzuki

Sidonia Command

Yuhata Midorikawa | Ryouko Takahashi | Ichirou Seii | Ochiai Clone

Immortal Ship Committee

Kobayashi | Lala Hiyama | Hiroki Saitou | Yure Shinatose | Ochiai

ET Research Center

Numi Tahiro | Yure Shinatose

Toha Heavy Industries

Sasaki | Shinsuke Tanba | Shijimi

Kunato Developments

Norio Kunato - Mozuku Kunato


Teruru Ichigaya


Tsumugi Shiraui - Kanata

Gauna 487 | Gauna 491 | Gauna 492 | Gauna 493 | Benisuzume | Placental Hoshijiro | Ocarina | Gauna 541 | Large Mass Union Ship | Lem Gauna Wall | Lem VII Gauna | Aulos

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