I'm building a world where kaiju-sized creatures exist alongside regular-sized creatures. How these kaiju don't crumble under their own weight doesn't matter, and can be explained away by them being biologically separate from the regular creatures and not made of what everything else is made of. Aside from that, they're basically giant organisms that live, consume, reproduce, and die.

The thing is, these kaiju are a late addition to my story, and the story could work perfectly well without them. The setting originally is a low fantasy medieval world where various fantastic megafauna coexist with people. However, these kaiju fit the themes of the story and make the story feel more fantastic. And I just like seeing them in the background, or at least the marks they leave behind, like giant footprints and skeletons (the story is for a comic by the way, and seeing gigantic versions of normal things is always cool).

My question is, what should I pay attention to regarding these kaiju so I can arrange them to not change the world in a significant way, at least until I want them to?

Some problems and possible explanations I have thought of:

  • How are they not destroying settlements all the time? They're big and slow, so they're easy to spot and avoid. Also, maybe they move in predictable pattern and avoid certain areas, so that's where civilizations grow.

  • If they are made of super strong exotic materials, why are people not using it to make stuff? Maybe the hard parts like the bones are so hard that people can't do anything with them with the current technology. The less hard parts like flesh and blood might be toxic or dangerous in other ways to regular life that people wouldn't want to touch them.

  • Why are these kaiju not what everyone in the story is talking about? Maybe they're rare enough or live far enough away from civilization that they're not a concern for most of the time. Like solar eclipses or hurricanes, people don't talk about them until it's immediately relevant, like when they're coming near a settlement or when people have to move through their territory.

Anything else I should think about?

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    $\begingroup$ "Don't crumble under their own weight" "Not made of what everything else is made of". Their skeletons are made out of limpet teeth material? royalsocietypublishing.org/doi/10.1098/rsif.2014.1326. Although I am not sure about the compressive strength. $\endgroup$ Commented Jul 23, 2023 at 3:40
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    $\begingroup$ godzilla got it right, if they spend most of their time in the deep ocean, humans might not even realize until you reach modern technology. $\endgroup$
    – John
    Commented Jul 23, 2023 at 20:17
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    $\begingroup$ I strongly recommend reading goodreads.com/book/show/57693406-the-kaiju-preservation-society The Kaiju Preservation Society. Scalzi does a great job identifying the practical characteristics of how kaiju might exist with vaguely realistic physics. You won't be able to have them live in the same world as humans with minimal impact. Their food requirement, all by itself, would dominate the ecology in any area they stood. $\endgroup$ Commented Jul 23, 2023 at 22:43
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    $\begingroup$ VTC:Needs More Focus (You're allowed to ask one and only one question). For the record, elephants are just small kaiju... but they cause all the same problems you're talking about. What is it about elephants and their association with humanity that doesn't answer your question? Keep in mind that your kaiju are only different compared to elephants if you choose them to be. Those choices will answer most of your questions. $\endgroup$
    – JBH
    Commented Jul 25, 2023 at 17:37
  • $\begingroup$ I suggest Kevin was well on the way to being wholly correct. What 'can be explained away by them being… not made of what everything else is made of' is 'the basic laws of physics'. If you could explain away the basic laws, why would you worry about a trivial Question like how kaiju could exist without altering 'civilization'? How do you see 'in nature' as different from 'according to the laws of physics? $\endgroup$ Commented Jul 31, 2023 at 20:50

15 Answers 15


Huge. Slow. Indestructible.

enter image description here

You don't need to change the world too much, provided you don't make the Kaiju too common.

Think of your titanic monsters as a different type of hurricane. They do much the same thing. In fact, since this is my answer, and I can do what I want, I declare they do exactly the same thing. Compared to the garden variety hurricans, Kaiju are exactly as

(a) huge

(b) dangerous

(c) common

(d) unstoppable

(e) indifferent to humans.

Kaiju eat grass and pay no heed to us puny humans. Every few years, by sheer fluke, a Kaiju walks near your city and you all just have to deal with it and rebuild after.

Despite this, real people keep building cities in places where there are hurricanes. It stands to reason they would keep building them in places with Kaiju.

If they are made of super strong exotic materials, why are people not using it to make stuff?

You can either (A) completely ignore the material concerns and how these giant monsters can support their own weight or (B) declare the material is so strong that people have no way to use it. It is stuck inside a living kaiju and then it is stuck inside a dead kaiju. We cannot break the skin.

  • $\begingroup$ Maybe I should watch Shin Godzilla again... $\endgroup$ Commented Jul 25, 2023 at 1:57

They do destroy settlements. From time to time. But then, settlements are also destroyed by barbarian invaders, famine, plague, volcano eruptions, flood, and forest fires. From time to time.

The inhabitants of your world (especially the 'dumb rural peasants') feel that the world is a scary place and that they have no control over things which might happen to them. Except trust in their clergy and their own warlords.

You mentioned these kaiju as being a separate biology. For a fantasy story, don't. Knights are called upon to protect the hapless peasants from less-than-skyscraper-sized megafauna, and mostly they succeed. From time to time, the first local knight to fight a monster dies, and the king has to send a hero and/or a small army. And then there are those slightly larger ones where the king's troops can do nothing but mitigate the disaster and hope the monster goes away, perhaps aided by a deliberate forest fire to make things unpleasant or by rounding up lifestock to make food scarce. At which point, someone steps forward to claim sort-of victory, and the order of things is right again. The peasants have been protected by their overlords, which is why the peasants owe their overlords feudal dues.

By choice, kaiju live where slightly smaller herbivore megafauna roam the land. Getting a full belly by hunting individual deer or elk is so tedious, and grass does not have enough calories. And as it happens, human settlements drive those slightly smaller megafauna away or kill them.

It would help with the survival and stability of civilization if the larger the kaiju, the less likely it is to wander into civilized areas. Here there be dragons and all that.

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    $\begingroup$ I've already written all of the things you mentioned for the main plot of man vs. animal. I want the kaiju to be there in the background and not bother the main plot except when I want them to. $\endgroup$ Commented Jul 22, 2023 at 14:21
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    $\begingroup$ It could also be the other way around and civilization doesn't set up shop (at least for particularly long) in Kaiju country. And, if one of the big ones gets ousted from their territory, that means a kingdom or two worth of refugees for everyone else to deal with. $\endgroup$
    – HAEM
    Commented Jul 23, 2023 at 18:52

People do use Kaiju parts to make things. Only, you need a dead Kaiju to properly mine it. Because Kaiju and human habitation get along like water and elemental sodium, a dead Kaiju will by necessity be far from the edge of cultivation.

If the Kaiju didn't die in the process of pushing back said edge, job number one is even finding a carcass. You will then have to bring a lot of mining equipment across trackless wilderness, along with provisions for the duration of the mining operation. During the operation, you need to worry about any inimical qualities of a Kaiju's bodily fluids, as well as the fact that carrion eaters will be drawn to the carcass. These carrion eaters will include Kaiju.

Finally, after the bone is extracted, you will need to haul it across that same trackless wilderness back to civilization. All of this combines to make Kaiju Ivory one of the most expensive materials in your world, and artisans that can work it are rare. Therefore, it is mostly reserved for ostentatious decoration and for really fancy weapons. The same applies to anything else that a carcass might yield.


Homo sapiens is the only invasive species having a large body and which has a sort of compulsion to invade and destroy any environment.

All other species prefer, when possible, to just get their sustenance from the environment where they are and leave other species enjoy what is left. Sure, elephants can make a mess when they charge in group, but they do so only when enraged. A buffalo stampede can flatten a prairie in the snap of a finger, but won't do it just for the fun of it. A blue whale jumping out of water can crush a medium sized boat, but won't do it just because it is bored on an evening.

Wild animals in particular have learned that avoiding humans as much as possible is better for them, in the same way we have learned that pic-nicking on a ant hill is not the smartest of the ideas.

Your kaijus are the same: they don't have the innate instinct to smash things for fun and have learned that avoiding the humans is preferable for the sake of enjoying a quiet after dinner.

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    $\begingroup$ @NoName Cats are just an easy example I've personally seen. It's a stupid idea perpetuated by people who don't have experience dealing with animals that humans are uniquely destructive, unpleasant, or mischievous. $\endgroup$
    – Jedediah
    Commented Jul 24, 2023 at 2:22
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    $\begingroup$ "All other species prefer, when possible, to just get their sustenance from the environment where they are and leave other species enjoy what is left." You've never seen deer destroy an environment. $\endgroup$
    – RonJohn
    Commented Jul 24, 2023 at 6:05
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    $\begingroup$ This answer has no basis in biology. EVERY living being has a compulsion to spread. Many of them try to change the environment to fit them better. Quite a bit of them do inflict "cruelty" out of boredom (humans are not the only "asshole" species, nor are we the largest; just look at doplhins), And wild animals avoid humans now, but didn't do so in ages past. We just selected out all those who didn't avoid us... $\endgroup$
    – Negdo
    Commented Jul 24, 2023 at 12:48
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    $\begingroup$ This answer is based on a false and fundamentally offensive premise. Elephants wantonly topple trees, beavers build dams, chimps literally premeditate murder of their rivals, just to make a few examples. All species spread wherever they can successfully breed. Humans have created more than destroyed, clearly. Human expansion is not "invasion" and humans do not have a natural "compulsion to destroy", or whatever else this anti-human ideology might make up. $\endgroup$
    – user458
    Commented Jul 24, 2023 at 14:01
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    $\begingroup$ "All other species prefer, when possible, to just get their sustenance from the environment where they are and leave other species enjoy what is left. " You mean like the Elephants that continually reshape the grasslands of the Serengeti by leveling down the extant forests? $\endgroup$
    – ouflak
    Commented Jul 24, 2023 at 15:19

You're thinking too small

You are probably thinking of beasts that are just big enough to go over city walls with ease. Beasts in the size range that contains Godzilla and King Kong, for example.

In literature there are plenty of creatures orders of magnitude larger, and the way they interact with humans is very interesting. The nature of such interactions means that for the most part they just... Exist. Interesting things usually happen over aeons, or are tied to fate or prophecy, which is why catastrophic things don't happen very often.

In Avatar: the Last Airbender/Legend of Aang, there are lion-turtles (think chinese lions with turtle shells), beasts so large that when swimming they are mistaken for islands. People built entire cities - not towns, actual cities - on their backs. Lion turtles were intelligent, kind, and acted to protect humanity.

In the Discworld series of books, the whole world is a flat planet that stood on the back of four giant elephants. The elephants in turn stood on the back of a turtle who was longer than the planet was wide. These beasts' movements take geological time to complete, and they are generally not visible except from the rim of the world - a very dangerous place. The turtle is generally harmless but scholars keep discussing whether it is a male or female. If the latter, then the world might end when the turtle eventually copulates, as the planet will be smashed in a phenomenon called The Big Bang.

In greek mythology, the world was carried by a titan called Atlas. I suppose earthquakes might happen whenever Atlas had chills, and it may have been quite a swing when he placed the world on Hercules's back (specially given that Hercules was human sized while Atlas was humongous).

And in Judaism Leviathan is a sea monster that, according to the Babylonian Talmud, is three hundred miles long (483 km, approximately). That is about the width of Britain at its widest or second widest part (I don't remember exactly which), going from the west coast of Wales to the east coast of England. Not only cities but a couple countries fit into that length. Leviathan's usefulness is that once the Lord is done with the world, the just will eat the monster in a banquet.


The super-exotic materials is simple: they involve danger to humans. Ironically enough, it doesn't even have to be real. If people used the bodies and got hit by a coincidental plague, or even flood, they might be put off them. If it happened again -- and memory is great for things happening in conjunction, while ignoring isolated things -- that would build up to a superstition. (How could it cause a flood? Punishment for dealing with a diabolic monster as if it were an ordinary beast.)

And that's on top of the way that it might have heavy metals, or radioactive material, or simple organic poisons.

One notes that famines, plagues, floods, and other disasters are simply part of life in this era. This is just another. Look at tales of dragons and other monsters plaguing settlements to generate their attitude. (Presumably sacrificing the princess would not help, but that would probably be interpreted as a mistake in how to appease.)


The Kaiju are ancient creations of a lost civilization of high magic and follow predictable rules.

An ancient civilization which had more access to advanced magic created them, and set them loose to follow arcane rules that no one knows. This allows them to be easily controllable and manageable.

  1. They don't normally attack people. Whatever their goals are, for the most part they stay away from population centers. While failures in their biological programming happen especially when it would be interesting for your story, for the most part they are not a major setting element. Some exceptions may exist for interesting towns where the natives have managed to divine some hidden rules of the creatures and lured them to be mounts or such.

  2. They make extensive use of rare earth elements and radioactive elements to be functional, and while they are safe to touch, when dying they tend to leak a lot. They're not safe to touch. By the time they are more safe and are just a collection of bones they tend to have lost enough of their exotic properties that they're not as useful.

  3. They have no major use to most civilizations so they aren't a big topic. They mostly avoid people, don't provide useful resources, and don't do things that help people much. As such, they are mostly just seen as natural landmarks, like moving mountains or storm clouds. Certainly the subject of speculation and wonder, but not something that most care deeply about.


It might be best to consider what kaiju can't do in your world. This would limit them (and limit your options), but it would make for a more "realistic" feel as omnipotent creatures are a little boring in that you can't really deal with them and the whole show becomes a just so story.

Perhaps kaiju can't swim as they are too heavy and they are restricted to a large island or continent until a volcanic upheaval allows them out by raising a land bridge.

Perhaps kaiju are simply content to stay in the area where the xyz tree fruit they live off grow. People might then control the kaiju to a limited extent by burning or cutting down xyz trees in border areas. A series of bumper years might cause xyz trees to sprout and grow all over the place beyond the inhabitants capacity to destroy them leading the kaiju to extend their range and come into greater contact with the human population.

Perhaps the kaiju are huge, but are also (somewhat) vulnerable and can be slain by powerful stinger type crossbows. This means they don't usually come too close to human habitation. Maybe until some people raid a kaiju settlement after which the kaiju turn nasty and attack mob handed perhaps with stout protective garments.


Because the kaiju are sea monsters rather than dinosaurs.

How are they not destroying settlements all the time?

Settlements are on land, and the kaiju can't get close enough to land to do much. Sure, there's more tsunami than on typical Earth, but that can be somewhat mitigated by walls and simple settlement placement (kaiju will likely make seaports less desirable since shipping is an even riskier business).

If they are made of super strong exotic materials, why are people not using it to make stuff?

Because they can't harm the kaiju, and kaiju fights lead to the stuff being out to sea. Simply making useful kaiju stuff dense (so it sinks to the bottom of the ocean) would be enough to put it out of reach of medieval tech. Maybe a scale or something will wash ashore once in a blue moon to develop the fantasy mystique, but this is seen as a random blessing rather than something that men could harvest.

Why are these kaiju not what everyone in the story is talking about?

Like any sea monster, it's bad luck to invoke their name. Most commoners don't go out to sea, so they're not directly impacted. The kaiju are some vague "seas are deadly" rumor that most people don't believe.


Kaiju are easily repelled.

We tend to think of kaiju as big dangerous monsters with a disregard for (or animosity towards) humanity, but there's no reason the opposite can't be true: kaiju are skittish. Just big ol' babies. Or humanity found something that kaiju very much dislike and so repelling them is super easy.

Thus, kaiju don't significantly alter civilization because civilization has found that they don't need to deal with them, for the most part. Maybe even a cornered kaiju doesn't fight back. Maybe it just gets stressed and dies, like a goldfish.

You know how towns tend to have giant clock towers or church bells? Turns out, these were the kaiju repellant. That reverberating "GONG" noise just really upsets them and they move away from it. If they can't move away from it, it stresses them out and they die. Having something like that which rings regularly -- oh, say, on the hour -- makes your town totally immune to kaiju, which is why in every new settlement, the first thing they build is a big bell tower.

  • $\begingroup$ I believe in regards to myths about trolls, church bells (at least initially) affect trolls because of their association to Christianity but in more modern myths the bells tend to cause them physical pain. Cool idea $\endgroup$
    – roan
    Commented Sep 12, 2023 at 16:30

Your kaiju start off a lot smaller.

In many fantasy stories, dragons are a kind of kaiju and they have this feature: they tend to be very big, very old, and very rare. They are very rare because they have to be very old in order to get very big. Your kaiju could be the same. Maybe you have certain creatures, like turtles or raccoons (for instance), that are a normal size when they are a normal age. Only the rare turtle that survived on a deserted island for a thousand years, or the rare raccoon that settled in a hidden mountain valley for an eon, would grow to such enormous size. They would consequently be very rare, often one-of-a-kind freaks of nature, and they wouldn't produce more like themselves within the lifetime of a human civilization.

As long as your kaiju are rare, they won't likely have a major effect on civilization, except in the local area, because the world is really quite vast. I mean even a mile-long monster is only a mile long, if you think about it. There may be a seafaring people who worship the giant turtle, or a mountain tribe that feeds its enemies to the giant raccoon, but this is necessarily remote from your major cities and populated areas.


How large is large in terms of Kaiju.

Simply considering the question from the point of dinosaurs may provide some perspective / solve your issues.

Titanosauria could reach upwards of 120 ft long, and 70 tons in weight. Maybe 20x an elephant. And even with those sizes, estimates on food requirements are that there might have been a few to 10's per sq. km.

Biology can actually support significantly large sizes than just elephants, without creatures crumbling in on their own legs. Ampelosaurus legs (an image example of a Titanosauria member) are not even that different in body scale from an elephant.

If we actually look at the bones of these specimens, they're strong, yet not space material / magical sci-fi strong. The dinosaurs apparently even had enough carrying capacity to have armor, scales, and spikes at those sizes.

  • No need for exotic materials and affecting society.

Other concerns: "How are people not talking about them." There are deer and elk everywhere in America. They're relatively large compared to humans and extremely dangerous to automobiles. Yet I don't talk about them all the time. I talk about them when they smash through the windshield of my car, or eat my back garden. Otherwise, there's some deer. Occasionally people go hunting. Deer meat's a thing. But its too inconvenient to be mass market. Kaiju can be similar. "Duh, there's Kaiju... You'd have to be blind not to notice." They just get talked about like something people are used to and accept.

"Destroying stuff." Similar argument as the deer and elk. They do destroy stuff. They're just not actively malicious. They might think your tree or cow are delicious, and you'll wake up to find out you don't have an oak tree any longer. You occasionally have to drive them away like bears up in Alaska. Bears aren't malicious, they're just really dangerous under the wrong conditions.


Kaiju generally keep to themselves, grazing peacefully, because their evolution of gigantism has made that the most efficient path.

Setting aside the usual square-cube laws that come with sizing up creatures, let's look at real-world examples. Whales are probably the best ones here: they're the most massive creatures on the planet (probably ever to exist on Earth), and their size affords them a number of advantages that all add up to what you're probably looking for.

In this, I'm imagining Kaiju on a truly massive scale: one the size of a building would be downright shrimpy. Most are anywhere from the size of a city block to being able to serve as a small island.

  1. Many of them spend a lot of time sleeping, sunbathing, etc. A creature that big is going to be pretty slow, so they'll likely not need or want to be doing any more motions than they have to. A snake will eat a mouse and then sit in its nest digesting it for a week or two—scale that up to some of these Kaiju (albeit not necessarily meat) and you can easily have them in the same place for weeks, and even when they do move, their movements are slow and deliberate. (Plus, this plays nicely into the "sleeping dragon" trope so common to the myths of Kaiju.)
  2. Their massive size actually makes their metabolism more efficient, so while they may eat a lot of food, they don't need to go hunting for it. This also incentivises herbivory, because they're so large that it's easy for most creatures to hide from them, and they're so slow that most everything can outrun them or at least dodge. Plus, plants or plankton/similar are so much easier to get in large masses.
  3. There may be a range of sizes for these creatures, but as a rule, they're so massive that no other creature would stand a chance hunting them. Some of the larger ones wouldn't even notice a regular-sized creature attacking them, since they're the size of city blocks. A giant turtle-esque creature (that might have dirt and plants growing on its back due to its size and age) would be pretty unappetizing to most, especially considering how thick its skin is (let alone its armor) and it's far more likely to crush anything willing to get near to it by accident than they are to even catch its attention.
  4. These Kaiju are usually in places humans wouldn't want to be, just by their differing goals. Kaiju generally want to have a territory they can rest and a large area of readily-available food—the thick woods untouched by civilization or the deepest parts of the ocean are perfect for them. Their size and fantastical nature might even let them live in incredibly inhospitable environments, like in the crags of a semi-active volcano. Humans are usually perfectly willing to let them have their territories, and that helps feed into the "guardian of the wilds" trope that Kaiju often exhibit.
  5. Only the smaller Kaiju are going to be anywhere near predatory or aggressive, and those will probably be mostly seabound. Of course, when I say "smaller", I still mean something the size of a whale or larger, but probably not much more than a medium-sized passenger jet. The deep seas are a much better fit for an aggressive Kaiju, since the open sea makes it hard to hide from them and the water means they can move more efficiently, as opposed to lugging around all their weight on land. This means that you'll occasionally have an aggressive sea monster, and maybe a few kinds even come onto land occasionally, but overall most people live on land, and thus far away from any aggressive Kaiju species.

Our own folklore if full stories of big things that go bonk in the night:

  • dragons
  • giants
  • beware of fungie rings or you leave the world for hundreds of years
  • do not climb the bean stalk or touch the golden giant goose
  • "here be dragons", giant watersnakes or turntles that eat whole ships of the unwary
  • areas that when entered have a good chance to vanish you and yours for good

Like any species taken from their biome, your kaiyu are an ivasive species - fallen through the gaps in space-time-magic. There are ever only a few and only if they impact live enough the local rulers will put together a sizeable force to deal with them.

If left to their devices they vanish again - traveling to where ever they came from - using this world of tiny things just to pass through - if voluntarily or by happenchance? Who knows...

If one has to be killed, spoils go to the victorious kings, huge ribs used to build fancy cathedrals or tombs to the heros.


You asked multiple questions here, I'm going to only answer the "how they are not used by people" one, and the answer is that while their bone/skin/whatever is incerdiably though it also spoils rapidly after their death, what use is a great armor if you have to hunt a building sized monster to get it and even then you only have 2-3 days where you can use it before it deteriorates?


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