Sorcerers

He started raising his pistol, but the lightning from my wand was faster. It arced all over the room before finding his body, and the man fell, twitching. I took both his weapons, but ignored the keychain. Too fiddly, and there was no time. The lock to the cell door turned into rust under my touch. Wisely, neither Sal nor Manfredo asked any questions while I armed them and led them up the stairs, then out the gate, past a human chain that ferried buckets of sand inside as fast as they could. We were going the wrong way, leaving behind the only means of calling down a shuttle, but that was no longer an option.

— Little Magic

Magic is real in this galaxy, and it's as dangerous as it is useful: a volatile, hazardous non-material that's highly toxic to most living beings. (Or at least those originating on Earth: we can only speculate whether aliens even have their own form of magic.) Humans die within hours of exposure, unless they happen to be dragonmoprhs. Little else can save them.
Except for one thing: if the victim is very young, at most a few years of age, a combination of gene hacks and specialized medical nanobots has a chance of saving their life. This procedure requires advanced facilities and lasts for months or years if it succeeds at all. The risk of failure is so high, exposing a child to raw magic on purpose is considered attempted murder in most civilized polities.
Survivors of the procedure gain the ability to cast spells just by thinking of it (see Magic of the stars for details), at the cost of having a frail body. Usually they also sport visible body alterations, such as pointed ears, a tail, or patches of skin covered in scales. As each sorcerer has a different balance of gene hacks and nanobots, they are all unique. But they can't have any cybernetic implants, because magic messes with technology, and their nanobots don't get along with any other type.
Sorcerers die if the raw magic in their bodies is successfully dispelled, or if they are cut off from ambient mana for too long. (See: magic). Loss of their nanobots is survivable if they can be given a replacement load soon. There is no way a sorcerer can become baseline again.

Genetic Ancestor(s)

• Transhumans