Origins of the Planetouched
If you ask someone how the Planetouched got that way, most folk will tell you that it's due to their anscestry. If you go back far enough in a Tiefling's family tree, they say, you'll find that one of their anscestors was a Baatezu or a Yugoloth or some other kind of lower planar creature. Likewise, if you go back far enough in an Air Genasi's family tree, you'll find that one of their anscestors was a native of the Elemental Plane of Air, such as a Djinn. And sure enough, that's the most common way to become Planetouched.
But that ain't the only way...
Each one of the Inner and Outer Planes has permanent settlements in it. No matter how deadly a plane might be, you can count on there being at least a few permanent residences there. It might be a huge metropolis like the City of Brass, or it might be a town like Madhouse on Pandemonium, or it might be a small citadel like the Dustmen's floating retreat on the Negative Energy Plane. Even the Plane of Vacuum has a few small settlements of barmy sods who live there.
Each one of the Inner and Outer Planes also has a fundamental nature that pervades and suffuses every particle of every location within the plane. The Plane of Smoke, for example, isn't simply an infinitely big space filled with smoke. It's an infinitely big space filled with the idea of smoke. And while a basher living on the Plane of Smoke may be able to keep the smoke out of his kip with magic, there's no magic around that can keep out the idea of smoke. Because the idea of smoke is what the Plane is all about.
For those who have already been born, being constantly suffused with the fundamental nature of a plane doesn't have much effect. The process of being born tends to give a person a sense of self that's hard to change. Even babies fresh from the womb are already starting to define themselves on a very basic level. And once you start defining your sense of self like this, the fundamental nature of the plane you're living on won't have much affect on you.
On the other hand, children who are still developing in the womb don't have this sense of self. As a consequence, it's possible for a child to literally be touched by the plane while developing in the womb. Humans are more likely than any other race to have this happen, but it can happen to any race. And even for humans, it's a rare occurrence -- the overwhelming majority of the folks born on the planes are of the same race as their parents, and show no signs of being Planetouched. But every so often, two otherwise normal parents will produce a Planetouched child. That's just the way of the Planes.
Frequency of Genasi Types
The most common Genasi are those who have their origins in the four Elemental Planes: Fire, Earth, Water, and Air. This is because the most common way to become a Genasi is by having an elemental anscestor. And since the four Elemental Planes each have a well-represented race (specifically, Genie-kind) that can interbreed with humans and demihumans, Genasi related to these planes make up the bulk of the Genasi found in the Multiverse.
The Para- and Quasi-Elemental Planes and the Positive and Negative Material Planes, on the other hand, tend to be limited with respect to the number of native races capable of interbreeding with humans and demihumans. Some of these planes have no races whatsoever which are capable of interbreeding with humans and demihumans (or, at least, no known races), and so Genasi from these planes occur only when a child of two otherwise normal parents is literally touched by the Plane while in the womb. In these cases, planes with a large number of non-planar settlements will produce more Genasi over time than Planes with few non-Planar settlements.
As a consequence of these differing origins, the various Genasi can be ranked according to how common or rare they are. Inner Planes with races capable of interbreeding with humans and demihumans and which possess many large human and demihuman settlements will produce the most Genasi. Inner Planes with no races capable of interbreeding with humans and demihumans, and which have few permanent human or demihuman settlements will rarely produce Genasi.
- Common: Fire, Air, Water, Earth
- Uncommon: Smoke, Ice, Mineral, Lightning, Steam
- Rare: Ooze, Magma, Negative Energy
- Very Rare: Radiance, Ash, Dust, Salt, Vacuum, Positive Energy
Genasi are immune to any baneful effects which spring from the basic nature of their native Plane. Fire Genasi aren't hurt by normal fire, Ooze Genasi can swim and breathe in the mud and muck of the Plane of Ooze, Negative Energy Genasi aren't affected by the life-draining energy of the Negative Energy Plane, and so on. Furthermore, these immunities extend themselves to similar manifestations outside of their native plane. Magma Genasi, for example, are not harmed by Magma, regardless of whether they're on the Plane of Magma or if they're in a volcano on some Prime world.
However, some spots within a particular plane are dangerous even to those native to the plane. The Plane of Fire has hot spots that are too hot even for Fire Genasi, the Plane of Ooze has large patches of acidic slime which can affect Ooze Genasi, the Plane of Smoke has clouds of poisonous vapors which can affect Smoke Genasi, and so forth. In general, each Inner Plane has one or more areas that are dangerous even to natives. Genasi are not immune to these areas, despite being unaffected by the more common aspects of their native plane.
Finally, note that these immunities only extend to mundane manifestations of the particular element. Ice Genasi are immune to the effects of normal cold, but can still be hurt by magical cold.
Common Racial Traits of the Para- and Quasi-Genasi
A common theme that seems to be universally true for all Para- and Quasi-Genasi is their curiosity about the Multiverse. Most folks think that this inquisitiveness is just a racial trait common to all Para- and Quasi-Genasi, but it turns out that this is something of a misconception.
The life of a native on the Para- and Quasi-Elemental Planes is profoundly and fundamentally different from the life of just about anyone else on the Planes. To illustrate this point, consider the life of the average resident of Bytopia. Aside from the fact that the other layer of the plane is hanging directly overhead, living on Bytopia isn't much different from living on any of the Upper Planes, nor is it substantially different from living on many Prime worlds. There is grass beneath your feet, sky above your head, homes, rivers, lakes, oceans, animals and plants that would be familiar just about anywhere, and so on.
Now consider the life of a Para- or Quasi-Genasi. On the Inner Planes, there's no ground, nor sky, nor rivers, lakes, or oceans. In fact, there's nothing but an infinite expanse of the plane's particular element (or para- or quasi-element), broken up by the occasional pocket of matter from one of the other Inner Planes. This alone would explain the reaction that most Para- and Quasi-Genasi have when they make their first trip outside of their native plane, but there's another factor which contributes to their reaction: Aside from the four Elemental planes, most Inner Planes don't get a lot of traffic. So not only does your average Para- or Quasi-Elemental Plane not have much variety in the landscape, it also doesn't get much in the way of visitors from other places.
You can imagine, then, what it must be like for a Para- or Quasi-Genasi when they step foot out of their first portal. Suddenly they're confronted with sights and sounds (and smells) they've never encountered before. And not only are they having to cope with the sudden presence of all these new sensations, but they're also having to cope with the absence of whatever element it was that made up their home plane. If you've spent your entire life surrounded by an infinite expanse of salt, you're going to find it very strange to live in a place where salt is something you'll only find in little shakers on the tables of various restaurants and inns.
As you might guess, the first trip a Genasi makes off of their home plane is usually very disorienting. Most Para- and Quasi-Genasi can't adjust, and so they end up taking the first portal back home. But some Para- and Quasi-Genasi find themselves drawn to the planes, and find that their curiosity about the Multiverse exceeds their desire to go back to their native plane. So when a Planar meets a Para- or Quasi-Genasi off of the Genasi's native plane, the Genasi is almost always one of the curious ones.