Pacific Rim Wiki
Pacific Rim Wiki

Pan Pacific Defense Corps. Kaiju Warning sign

The Kaiju (怪獣 kaijū?, Strange Beast) are a race of amphibious creatures[1][2] genetically engineered by the Precursors, a sentient race from the Anteverse. In 2013, the Precursors opened a portal between dimensions at the bottom of the Pacific Ocean, allowing the Kaiju to enter Earth and begin their assault on humanity. As biological weapons of warfare, Kaiju are extremely hostile and toxic creatures designed with the intention to wipe out all humankind.[3]


Triassic Period

During the Triassic Period, the Precursors attempted to colonize Earth, but the environment proved to be uninhabitable for them and prevented them from surviving on the planet. As a result, they decided to put their plans on hold and wait until Earth's environment was just right for them to colonize.[4][3]

Creation of the Breach

The progressive pollution of the Earth's environment by mankind made it possible for the Precursors to survive on the planet and colonize it. In response, they created a race of amphibious creatures, biological weapons later known as the Kaiju by the humans. Shortly thereafter, the Precursors create a portal that bridges their universe to Earth on the floor of the Mariana Trench.[4][note 1]


The Kaiju first appeared on August 10th, 2013 in San Francisco. The beginning of the incident was believed to be a 7.1 earthquake; however, a massive, three-hundred-foot creature, later known as "Trespasser," eventually emerged from the San Francisco Bay and attacked the Golden Gate Bridge. After destroying the bridge, the creature proceeded towards San Francisco and caused significant devastation; it cut a three-mile-wide path of destruction through the city. The massive creature then went on a 35-mile rampage across the West Coast that lasted for six days. It continued on to Sacramento and Oakland, causing massive destruction in its attack.[5] The United States and British militaries responded to the attack and battled the creature for six long days.

Despite the use of troops, tanks, artillery and jets, the combined forces of the two armies failed to kill the massive beast. On August 15th, the military decided on using tactical nuclear missiles in the hopes of bringing down the creature. They finally succeeded with three tactical nuclear missiles.[6] With the end of the destruction, three cities were left devastated and tens of thousands of people had died. The dead were mourned, the event was memorialized and humanity moved on. The incident in San Francisco was later known as "K-DAY"[6][3].


Trespasser's attacks on the three Californian cities was initially believed to be an isolated event.[3] But then, six months later, Hundun appeared and assaulted the Filipino capital of Manila. Four more months passed before Kaiceph made landfall at Cabo San Lucas and caused substantial destruction. As Kaiju began to appear in increasing frequency, nothing short of nuclear options proved capable of stopping them.[6]

Scissure then attacked Sydney on September 2nd, 2014. As Scissure neared the city, the Australian military lured it away and deployed a nuclear missile against it. The attack failed, and the creature proceeded towards the city and began laying waste to it. After three days, the military again dragged the creature away from the city, hoping to deploy another nuclear missile against it while sparing the city the effects of the nuclear fallout. The nuclear missile was deployed, but even though it killed the beast, half the city was destroyed by the blast.

It was clear that continued use of nuclear weapons was pyrrhic; the environmental devastation was far too great a cost. Therefore, after the Sydney attack, Dr. Jasper Schoenfeld began to contemplate how to protect the populace without resorting to nuclear weapons.[6] Inspired by his son's robot and monster action figures, Schoenfeld and Caitlin Lightcap managed to create a prototype that would lead to full production of the Jaegers.[6]


Numerous Kaiju attacked various cities along the Pacific Rim and were met with staunch resistance by the Pan Pacific Defense Corps' Jaegers. Over the next five years, Kaiju slowly adapted to the Jaeger's strength. However, it was the belief of the Defense Corps that the invading creatures were losing to the combined efforts of humanity.[3]

They remained unaware that Kaiju's specific reason for attacking large cities and populaces was to cleanse the environment of "vermin"; in this case, humankind.[7] While the first wave of Kaiju were merely scouts, it was the next one that were the exterminators. The information provided by the Jaeger battles allowed the Precursors to create Kaiju with specific abilities or strengths in a series of "waves". In accordance to their increasing size and strength, the Defense Corps created a "Category" scale, classifying Kaiju on the basis of toxicity and water displacement.[3]

By 2020, Category III and IV Kaiju were becoming common Kaiju to attack the Pacific. February 2020 marked the beginning of the Defense Corps' downfall in the war against the Kaiju when the Category III Kaiju, Knifehead exhibited the learning curve that allowed it to critically damage the Mark-3 Jaeger, Gipsy Danger and kill one of its pilots.[3]

As the Kaiju began to best the Jaegers, the United Nations put into motion plans to create a Wall that would isolate the Pacific Rim from the rest of the world in the hope that it would stop the Kaiju from spreading and began to move civilians further inland from the coastlines.[3]


There were thirteen Kaiju attacks in 2024 alone, resulting in staggering Jaeger losses. Hermann Gottlieb speculated in the aftermath of the assault on Sydney by Mutavore that the increasing appearance of the Kaiju and their attacks suggested that the emergence of Kaiju from the portal would increase until there were mere day or hour lulls in their attacks, leading to the "Double Event" and "Triple Event".[8][3]

Gottlieb's fears were later confirmed when his colleague, Newton Geiszler, "drifted" with a Kaiju's secondary brain in order to gain information in the K-Science Lab. Newton learned the first wave of Kaiju sent through the portal were meant to both test and weaken the boundaries of the inhabitants' defenses. The second wave of Kaiju would have adapted to the battle strategies of humankind and proceed to wipe them out in a mass extinction event.[3]

Leatherback and Otachi simultaneously attacked Hong Kong in search of Newton, and, during the process, destroyed two of the four remaining Jaegers, Cherno Alpha and Crimson Typhoon. The Triple Event later occurred during the mission to bomb the portal. Scunner, Raiju and Slattern all emerged from the portal to defend their masters from certain destruction at the hands of Striker Eureka and Gipsy Danger. The Kaiju and their masters, within the boundaries of the portal, were destroyed when Gipsy Danger's nuclear reactor was set to self-destruct. The destruction of the Breach ended the Kaiju War and destroyed the facility of Kaiju clones.[3]



How Kaiju are categorized with the Serizawa Scale.

Kaiju are creatures of a highly toxic nature and have been categorized on the "Serizawa Scale". Each Kaiju is classified into five different categories. Categories I and II represent the weakest of the Kaiju, while Categories III through V are the strongest. The Serizawa Scale measures water displacement, toxicity and ambient radiation levels given off by their bodies when they pass through the breach.[9] The fluid of a Kaiju is ammonia-based. Should they be killed in battle, their bodies are triggered to self-destruct immediately.[10]

Upon decomposing, their bodies release a noxious agent into the air known as "Kaiju Blue", their blood. Kaiju Blue has the ability to contaminate the air and its immediate environment, rendering it essentially uninhabitable. The blood of a Kaiju is highly acidic, corroding anything in its path. This makes it especially hard to gather samples safely for examination and experimentation. As a result, Jaegers have been equipped with weapons that cauterize wounds they inflict on Kaiju to prevent the spread of their highly acidic internal fluids[10]. As silicon-based organisms, the design of their bodies makes it difficult to determine and study particular parts of their internal systems.[note 2][10]

Kaiju are colossal in size, averaging hundreds of feet in height and thousands of tons in weight. Because of their tremendous body mass, two brains are needed to control the Kaiju's motor and cognitive functions. Bipedal Kaiju tend to possess multiple arms (usually two main arms and a smaller pair), the case ulna and humerus are visible and a bit spread, making it look like there were two forearms.

Their bodies allow them to adapt and dominate on land and water once they enter Earth through the breach.[11] Kaiju are able to breathe and survive in multiple types of environments, which include land, underground in extreme heat and high pressure, underwater and even in places without air, such as space.[3] As biological weapons, their anatomy is designed to be exceedingly useful on a tactical level.

Kaiju are also symbiotic, as they possess large, parasitic organisms that are attached to their bodies.[3][12]

Kaiju tissue is cloned from a single strand of DNA by the Precursors, who "build" Kaiju by fusing the sinew of body parts from other Kaiju creations together.[13] All Kaiju share the same genotype but have widely varying phenotypes. This results in anatomical similarities with another type of Kaiju as result of cloning.[note 3] Once created, Kaiju are pitted against each other. This process initially singled out those most ruthless in the forms of melee combat to be chosen. The surviving creations are then used as biological weapons in order to rid a chosen planet of its lifeforms so that they can colonize it.[4] Despite their nature as clones, each individual Kaiju is a unique specimen distinct from the rest of its brethren, resulting in highly varied forms and characteristics.

Over the course of the war, the Precursors improved the Kaiju, each becoming larger and more powerful than the previous. Later specimens, like Otachi and Leatherback, possessed unique biological weaponry, such as acidic and electromagnetic discharges in addition to the standard Kaiju's size, strength, claws, and teeth.[4][3]

Though their bodies breakdown fast, Kaiju organ Harvesters always move in quickly to harvest Kaiju parts to collect for themselves and sell on the black market. According to Hannibal Chau, every part of the Kaiju is usable; even Kaiju poop has a practical purpose.[3]


K-Science officers speculated that Kaiju are attracted to cities, locking onto centers of population by following urban runoff.[14]

Kaiju are highly aggressive creatures, especially when engaged in combat. However, they are not clumsy nor do they possess limited intelligence. Working through a hive mind system, the Kaiju can communicate instantly. This is similar to the way Rangers communicate in the Drift. Their ability to fight and attack in packs is demonstrated in their battle against the four remaining Jaegers, Gipsy Danger, Striker Eureka, Cherno Alpha and Crimson Typhoon.

Even during individual combat encounters involving a single Jaeger and one Kaiju, the creatures were able to demonstrate a degree of cunning and slyness. This was first shown during the duel between Gipsy Danger and Knifehead, during which the latter feigned death until its opponent had turned away from it, at which point it ripped the Jaeger apart, critically damaging it and killing one of the pilots.

Using their superior strength and intelligence, Leatherback and Otachi are able to coordinate attacks against the Jaegers. Leatherback and Otachi tear apart and crush Cherno Alpha[7] while Crimson Typhoon is taken out immediately by Otachi's tail when it destroys the Conn-Pod containing its pilots. Their role as weapons against the Jaegers is further exemplified when Leatherback uses its organic electromagnetic pulse organ to disable Striker Eureka. Near the Breach, while Slattern faces off with Striker Eureka, Gipsy Danger is attacked unexpectedly by Scunner and Raiju, proving that Kaiju are capable of planning and executing complex combat and ambush strategies.

List of Named Kaiju (Prior to Uprising)

Category II

Category III

Category IV

Category V

Category Unknown

Category Unknown

Non-Canon Kaiju



According to del Toro, there are nine Kaiju chosen and designed for the film, each one with its own personality and abilities. At least forty different Kaiju were designed in the process. Based on the silhouettes designed by the production team, del Toro would hold an "American Idol"-type contest and gradually eliminate the silhouettes they didn't like.

All Kaiju are based on familiar creatures in the real world, such as gorillas and sharks. The very design of the Kaiju in the film is meant to reflect and pay homage to actors who donned suits to bring monsters such as Godzilla to life.[15] One of the first Kaiju designs by Simon Lee was later used in propaganda posters for the film.[16]


The word "Kaiju" is a Japanese word that literally translates to "strange beast," but is often translated in English as "monster." Kaiju may refer to any bizarre creature, but in recent times Kaiju is typically associated with a genre of films originally made popular in Japan in the 1950's.

The most famous Kaiju in history is Godzilla. Other well-known Kaiju monsters include Mothra, Anguirus, Rodan, Gamera and King Ghidorah. Terms related to Kaiju include:

  • Kaijū eiga: A monster movie[17]
  • Kaijin: Human-like monsters.[17]
  • Daikaiju: A giant monster, specifically meaning the larger variety of monsters.[17]
  • Ultra-kaiju: Monsters in the Ultra Series[17]
  • Seijin: Japanese term for aliens, also frequently called Uchujin which means "space beings".


  • The "Serizawa Scale" is likely named after Dr. Daisuke Serizawa, the scientist from the original 1954 Gojira film who was responsible for the creation and deployment of the "Oxygen Destroyer", which finally killed the original Godzilla.
  • Travis Beachman cites the connection (or lack thereof) between the Dinosaurs and the Kaiju was made deliberately vague as it ties to nature of the Precursors.[18]
  • Travis Beacham describes the Kaiju as a "Darwinian Army".[4]
  • According to Tales From Year Zero and Pacific Rim, four Kaiju attacked between 2013 and 2014.[6]
  • According to the Pan Pacific Defense Corps timeline graphs, four Kaiju attacked in 2015 alone.[19]
  • In the novelization of Pacific Rim, the second Kaiju attack occurred five months after K-DAY in Hong Kong. The third attack occurred eight months later in Sydney.[20]
  • According to the novelization, Kaiju have reproductive organs.[20]
  • K-Watch officers assigned to Mariana Islands are responsible for naming Kaiju based on the shapes received by sonar. If not, their names are chosen from a database.[21]
  • It's possible that some of the Kaiju were originally alien wildlife or sentient species that were mutated by the various experiments performed on them by the Precursors (Onibaba, Karloff, and Hakuja are prime examples since their anatomy seems more natural in appearance).



  1. Pacific Rim December 2012 Teaser Trailer:
    Raleigh: “We always thought alien life would come from the stars, but it came from deep beneath the pacific — a portal between dimensions in the Pacific Ocean,”
  2. del Toro: So they figure out that the base of fluid of the Kaiju is ammonia-based. So how do they neutralize it? But it takes a while because, first of all, it melts the pavement, melts the structures around it, makes a noxious gas. By the time they get to a Kaiju, the first few attacks, they can't even get samples or corpses or pieces to analyze it. The Kaijus are essentially triggered to self destroy if they fall. So it's a very smart weapon.
  3. Travis Beacham: [...]Its partial similarity to the Kaiju on the cover is owed to the fact that some (but not all) of the Kaiju have variant incarnations. If you recall, Trespasser, Knifehead, and Scunner have essentially the same frames with different heads. And when Newt sees the Anteverse, we can see multiple Knifehead-types. Link