Genasi are generally similar to their regular D&D counterparts as found in the Player's Handbook. They are a planetouched race, linked to the primordial elemental energies of the elemental planes.
There are three theories on how they come to be: descendants born by the members of the mortal race who spent an extended time near a source of elemental power, like on one of the elemental planes, or near a rift to such a plane; a humanoid who born in the midst of a powerful elemental influence like a hurricane or a raging forest fire; or a genie of one of the elemental planes procreating with a human.
Genasi are derived from human bloodlines, and in the broadest possible sense, they still look like humans. Unlike other planetouched races, Genasi tend to have genasi children instead of whatever their original race was, and as such have developed a larger population and a distinct culture.
Genasi inherit the features of their parent ancestry, but skin of water genasi becomes shinier, hair of fire genasi resembles crackles of flame, and eyes of air genasi "glitter like gemstones". Some Genasi look more human, while some of them look more elemental.
Some genasi are delighted by "the attention their uniqueness garners them. But for others, even the most benign interest" is a painful reminder of their difference from the general population.
Unlike many planetouched races, genasi generally took pride in their unusual features. Furthermore, because of their elemental power, most genasi felt a sense of superiority over other races and even over other genasi—including those of the same element. This was not so much a matter of prejudice as it was simple fact—a simple mortal could not possibly understand the mind of one with elemental heritage.
The Genasi were created by the ever-churning chaos of the Realmshatter when the elemental planes bled into the material plane. Since they have genasi children, the planetouched race steadily grew in population and developed their own cultures.
Genasi populations tend to gather around the four primary elemental gates to the primordial realm, and towns often pop up near minor gates as well. Many genasi leave these communities to explore the world and settle elsewhere, and some genasi are simply born elsewhere randomly. A big exception to this rule is the city of Sergorod which hosts the largest population of Genasi despite its distance from the elemental gates. This was caused by frequent contact with the other planes during the city's history as well as a steady migration after the Cometfall.
"One begs the question as to how a city home to nearly a hundred thousand vivid and vibrant Genasi could be so overwhelmingly colorless."
—Uragan Ventorius, a world famous Air Genasi bard from Terros about Sergorod.
The four Genasi subraces are:
Air Genasi. Air genasi are either descended from the Djinn or descendants of humanoids who were exposed to the energies of the Elemental Plane of Air. Physically, they may be more lightweight than they appear, and they typically have light blue hair and eyes. They also usually have light blue skin, but pale, almost alabaster skin is also known, and some display odd patterns in their flesh. Air genasi are constantly surrounded by a faint breeze that affects their hair and clothing. They are mostly found on Aurial. They use the Genasi (Air) statistics as presented in Monsters of the Multiverse.
Earth Genasi. Earth genasi are descended from either the Dao or humanoids exposed to the energies of the Elemental Plane of Earth. Their heritage can manifest physically in a variety of ways, from constantly having dust falling from their bodies to having skin resembling pebbles, various metals, dark gems, or crystals. They are mostly found in Eteru. They use the Genasi (Earth) statistics as presented in Monsters of the Multiverse.
Fire Genasi. Fire genasi are descendants of either the Efreet or humanoids exposed to the energies of the Elemental Plane of Fire. hey do not hide their genasi heritage, which can show in skin tones of coal black, ash gray, or flaming red, and hair that is either fiery red or actual flames. In the throes of extreme emotion, their eyes may flare and their hair may writhe. They are mostly found in Eqos. They use the Genasi (Fire) statistics as presented in Monsters of the Multiverse.
Water Genasi. Water genasi are descended from either Marids or humanoids exposed to the energies of the Elemental Plane of Water. They tend to be wiser than other genasi, and take pride in their independence. Most have large, blue-black eyes, and they often have blue or green skin that is persistently moist. They are mostly found in the Blood Sea and the underwater cities of the Aethian Dominion. They use the Genasi (Water) statistics as presented in Monsters of the Multiverse.