Kapowch is a kangaroo-like creature infused with Fire magic, which naturally leads to certain problems with its pouch, no matter how you slice it. First of all, even if it’s open like a real kangaroo’s, the pouch will form a pocket of heated air. This hot air will then rise out of the pouch, making it less efficient as a heat source (and for Fire monsters, heat=power) than it could otherwise be, and potentially bringing dust and shed fur along with it (right into the face, urgh).

Accounting for this, it seems Kapowch will form some method of sealing its pouch closed, but then we have new problems. As this air heats up, pressure will build inside the pouch, potentially bursting it open. This necessitates the development of some way to relieve this pressure, but then I must ask the question; what will these method be?

This question is rather important to me, as it will determine how Kapowch will execute the Fireball attack it shares with its fellow Kaijura (type of monster), and as I lack a necessary understanding of biomechanics to solve it myself, for quite some time the best thing I could come up with is Kapowch shooting bursts of flame straight up from their pouch. Obviously, this is horribly inefficient and practically useless for self-defense.

Thus, in conclusion, How Would A Kapowch's Pouch Develop?


As bukwyrm so kindly informed me, the air sealed inside the pouch will become the same temperature as the Kapowch itself, and as that air heats, it will expand, building pressure until there is an escape of air. At this point, with the pressure released and the air already heated, the pouch should stay sealed.

I'm not sure this works, however. That escape of air will likely bring shed fur and dust into the Kapowch's face, and it may allow cold air in-hot air rises, cool air sinks, so what will end up in the pouch?

The problem is further compounded by the fact that Kapowch gain and lose Fire energy, as they use or build firepower within themselves, and will naturally draw heat from the air inside their pouch when they drop in temperature. This will result in heating and cooling within the pouch, which could very well mess with the perfect seal on the pouch.

And then, of course, considering that a kangaroo's pouch is basically a biological pocket and does not seal, one has to ask how a Kapowch's pouch could gain the ability to seal in the first place! Please note, the best answer will take such problems into account.

Further clarification:

Kapowch are insulated like a kangaroo, with fur and fat layers, and they convert ambient magical energy (mana) into

This internal heat source is depleted often; whenever a Kapowch generates or manipulates flame, it's drawing upon heat from that reserve to use as power. They can also generate heat using mana, but mana isn't static; it shifts and moves, diffuses and concentrates, so it isn't always reliable. Think of it like cell service. Because of this, a Kapowch's temperature will rise and fall, causing their air within their pouch to expand and retract, which will necessitate the development of some sort of pressure release system.

Think of it this way; the pouch is a heat battery. Whenever a Kapowch shoots a fireball or sets a fist ablaze for a searing punch, the battery gets drained. Ditto if the Kapowch is using it to stay warm. As the Kapowch grows, it becomes better at generating heat, so even if it keeps the air temperature otherwise constant inside the pouch, the air will continue to expand as heat builds inside said pouch.

I hope this helps, thanks for your input!

  • 1
    $\begingroup$ I am not sure there is a problem - if the pouch closes like a mouth does, the air inside will get heated to whatever temp the kapowch is - say the kapowch is 1200degreesC (whitehot) inside, then the air will expand to about 4 times its volume (if for some reason all the air inside the pouch was outside-temperature) - as soon as the overpressure overpowers the lip-seal, there is an escape of air, afterwards, when the air is already hot, the mouth can stay sealed. And : heat does not a fireball make - you need to tell us more about the fireball-making to take that into account $\endgroup$
    – bukwyrm
    Nov 18, 2021 at 14:00
  • $\begingroup$ @bukwyrm: I appreciate your enlightening points, but all the same, I am not sure there isn't a problem. That escape of air will bring fur and dust into the Kapowch's face, and could allow cold air to enter the pouch, plus there is the potential for the Kapowch cooling and heating as it uses or builds (literal) firepower. $\endgroup$
    – Alendyias
    Nov 18, 2021 at 22:33
  • $\begingroup$ I really do not get it: The kapowch has some internal heat source, and any part of its body is insulated, apart from the inside of the pouch - is that right so far? And the temp inside is...? And the fireball is created by... (spraying a fatty substance? old hair? what, how?)? $\endgroup$
    – bukwyrm
    Nov 19, 2021 at 6:16
  • $\begingroup$ @bukwyrm: it's okay, I'm figuring it out too. Yes, its body is insulated by fur, and perhaps special skin as well (a la Flaaffy from Pokemon). As for the temperature, I don't have anything specific in mind, just flaming hot-so like a typical fire-and I'm not entirely sure how fireballs are created, I will research it and get back to you. Thanks! $\endgroup$
    – Alendyias
    Nov 19, 2021 at 14:59

1 Answer 1


More context please

At the moment, you have a "magic-fire-kangaroo" as a premise, and then you dive into fine detail without passing through more general questions.

  1. Is this pouch similar to a lung?
  2. How is the heat extracted? Magically, physically moving hot air around?
  3. Would the pouch be belly-mounted as a kangaroo's is? Would it be reversed, to keep rain out?
  4. How heat-tolerant is this creature's biochemistry? Can the thermal-battery be kept inside its insulating layer of fat, or will its organs not cope with that?
  5. Do you mean "develop" as in evolutionary biology, or as in physical maturity?

With that being said...

Let's assume that this is an "open" pouch, with the intention of holding as much heat as possible and dispersing it very uncomfortably for the victim. We'll assume that the original creature of the species is magically created, so we don't have to worry about evolution. To launch anything from this, it will need to be almost-sealed and able to be pressurised, much like a sneeze or blowpipe.

Time for the hot-water-bottle!

Water has a very high thermal mass, about 4.2 kJ/(K L). This is why a cup of tea remains hot for a while, even when exposed to air. Your hands are largely water, and take a while to heat up in the sun for the same reason. Conversely, water has to shed quite a lot of heat to cool down.

Therefore, I propose that this pouch is something more like a cobra's venom-spitting ability, or a squid's ink-spray. Having near-boiling water (or even an actual steam-jet, depending on how controlled the heating effect is) sprayed in your eyes is bad news for an attacker. Using water also means that the mundane creature already has it as a significant part of its body-mass. If you're feeling practical rather than polite, this would also be part of the urinary tract.

Great balls of fire

Actual chemical-combustion fire is annoying and flashy for than actually effective. What your creature wants to do is cause pain (discourage) and burns (disable) with minimal effort. For that, I'd suggest that you allow it to magically shift heat from one part of the fluid bladder to another. Specifically, the part immediately adjacent to the opening. This lets you convert water to steam, raising the pressure immensely. This also adds the latent heat of vapourisation to the water molecules, and lets the temperature go above 100C (~373K) which is the limit for liquid-water.

(This is why pressurised water that boils over can be extra-problematic.)

Rather than the traditional coloured-fireball, the signature visual effect of this weapon would be a white vapour cloud.

For the growth-and-development, you can refer to mundane animals with this model.

I don't believe that I expected today to contain "a magic-fire-kangaroo pissing superheated steam", but that seems to (somehow) be a logical answer to your question.

I imagine there's also an above-average chance of kidney-stones and UTIs thanks to concentrated urea in the bladder, so these creatures are probably "naturally temperamental" (i.e. usually vicious and angry).

  • $\begingroup$ Thanks for your answer, it's very helpful! The pouch is a regular pouch that happens to trap heat, and has been developed to further increase its efficiency in that area. The heat is extracted magically, as Kapowch can transfer and absorb heat to and from their environment. And by develop, I mean physical maturity. $\endgroup$
    – Alendyias
    Dec 3, 2021 at 14:39
  • $\begingroup$ As for whether the pouch would be reversed or not, or how heat-tolerant it would be, I'll have to get back to you on that. $\endgroup$
    – Alendyias
    Dec 3, 2021 at 14:40

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