In this world – as with most worlds – pokémon are not simply creatures of flesh and blood, but innately extraordinary beings of mystical energy. This energy can take many forms, and has many uses. It is this energy that powers the combat techniques of pokémon, and which enables pokémon to evolve in a near-instant and retreat inside apricorn capsules. It can come in any of several different elemental 'types', and empower a pokémon's body, or be wielded like magic in countless forms.
This energy is sometimes called Infinity Energy, but its most common name is Aura. It is the life force of pokémon, and has properties that defy the laws of mundane thermodynamics. Many believe it is easier to understand it through spiritualism, than through scientific inquiry.
Pokémon can wield their Aura in countless ways, and achieve extraordinary feats with it, but usually only after growing strong through continuous striving – especially striving in battle. Everything from making elementally-charged attacks, to empowering their bodies, to surviving injuries all use the power of a pokémon's Aura. Naturally, these powers grow stronger as a pokémon grows stronger – those with a remarkably strong Aura can demonstrate enormous power, with great heroes and legendary pokémon being capable of things it would take dozens of ordinary 'mon to achieve. Myths tell of Saints who could stop a hurricane with their powers.
However, these are exceptional individuals, at the height of what is possible. The day to day lives of farmers and shopkeepers, artists, and builders, do not require such mighty feats. Nor is Aura without its own rules and limitations. For instance, one's species may govern the kinds of elemental energies they can wield, and how powerfully. It is also challenging to wield Aura outside of proven techniques, or to stay practicsed in more than a handful of strong techniques at once. Perhaps most importantly, the power of Aura energy does not make pokémon invincible by any means.
Your Aura will always protect you from attacks made with Aura energy, at least until your strength has wholly left you. Some 'mon are more fragile than others, of course, but even the weakest of pokémon can take a surprisingly powerful elemental attack and survive. Being in battle will make your Aura 'flare', and empower you to fight. Suffering attacks with a flared Aura will rarely result in any serious harm or lasting injury. When a 'mon takes enough attacks that they cannot safely continue to fight, their Aura 'breaks', and they faint. Pokémon are robust creatures, and recover quickly from fainting, ready to battle again. However, once a flared Aura has broken, pokémon risk being injured even by Aura attacks if they keep battling.
While elemental attacks always interact with Aura, mundane dangers do not. One's Aura cannot always protect a pokémon from normal kinetic and thermal attacks, drowning, poisonous substances, severe illness, and so on. A flared Aura will resist such dangers – and most adult pokémon will reflexively flare their Aura in an instant if attacked – but pokémon are wholly vulnerable to everything from raging fires, to exposure, to ordinary weapons, if caught unawares – or if their Aura has been depleted. In other words, pokémon can ward off all sorts of dangers if they're braced to do so or already fighting, but can still be badly hurt or even killed by natural causes. You should not be careless around deep water, wildfires, thunderstorms, blizzards, rockfalls, toxic gases, or any other such thing. Even if you have your Aura flared at all times, the power of 'Mother Nature' is far stronger than the energy of any pokémon's life force.
Still, one can keep their Aura passively flared. Aura flaring is easier, stronger, and more sustained the more powerful a pokémon becomes, and happens automatically during exposure to other flared Auras, i.e. using moves around pokémon will flare their Auras in response. Infant 'mon can often barely flare their Aura at all, typical adults will flare reflexively when in danger, but the very strongest pokémon have Auras so powerful that they are 'active' even in their sleep. One consequence of this is that sufficiently strong pokémon can walk through open flames, get struck by lightning, or even be shot in the back by a gunpowder rifle, and their Aura will still protect them as if it were a mere elemental attack.
Your Aura encompasses not only your body, but your immediate possessions as well. There are unclear limits to what counts, but pokémon routinely extend their Auras – as unconsciously as breathing – to include any clothing, supplies, tools, or adornments they may be carrying. This is why Teleporting does not, for instance, leave one's ear piercings behind. This is, thankfully, especially true for prostheses! Some items have Aura energy within them, either because they are the uncanny products of a mystery dungeon, or because they are a pokémon's body part, or treasured possession. For example, a Farfetch'd's leek is not simply an object they habitually hold, but a part of their identity, and filled with their very life force. However, one may only extend their Aura into so many so-energised objects at once! One must consciously connect with such items, and it takes concentration. This is called 'attunement', and it is the reason pokémon do not simply wrap themselves in dozens of layers of Tough Scarf fabrics!
Similarly, the rules and limitations about Aura-infused objects mean pokémon only have so much ability to channel their life energy into mundane energy. Using your life force to hurl a rock means that rock is, to some extent, an Aura-based attack. Weapons wielded with the strength given by Aura energy are necessarily Aura-based weapons. A strong enough pokémon, with a perpetually flared Aura, will passively infuse any weapon they use with their own energy. This is why swords and ranged weaponry tend to be used only by rank-and-file soldiers against each other, or weak 'mon such as wilds and civilians – they only outclass elemental attacks when used by weak 'mon against weak 'mon. In these circumstances, however, or when used against a foe who has been badly knocked out, they are lethal in a way that elemental attacks are not.
However, even under these circumstances, pokémon can still be tough to put down! While many are biologically mere flesh and blood without their Aura energy to protect them, countless others have adaptations or physical forms that protect them from weapons and mundane dangers, and any healthy pokémon is likely to heal easily and quickly from an injury. Consider that even a rifle bullet is likely to ping harmlessly off the armour of the average Rock- or Steel-type, pass straight through most Ghost 'mon, or fail to hit any vitals for all sorts of other species. Similarly, no fire is hot enough to kill a Magcargo, and no amount of water can drown a pokémon with gills. In short, there are few things in this world that can reliably harm or kill any kind of pokémon. Even being critically injured is survivable with swift medical attention.
Many strange and wondrous things are possible through the use of a pokémon's Aura – your own potential extends much, much further than you can see right now...