Kymeria, the Lost Daughter, 2nd Legion Primarch

 

Kymeria is the Primarch of the 2nd Legion, whose original name has been purged from history. There is no record of her "homeworld" and some think she grew up on Terra. It is, however, more likely that she was indeed found elsewhere, then brought back to the homeworld. She promptly escaped custody, killing an entire company of 2nd Legion Astartes as they sought to bring "their" Primarch into the fold.

The problem was that the 2nd Legion Astartes were all male, as they had been created from unmutated gene stock, whereas the Powers of Chaos had turned the Primarch into a woman. A kill order was issued from the highest echelons of command, and Kymeria was hunted down and slain in the underhives of the North Afrik Archipelago. 

Or was she? Some claim she escaped with the aid of the 11th Legion, the Granite Guard. I'm sure you've heard of this legion even though all records were erased...

Kymeria is physically larger than normal women, nearly the height of a male Astartes, but not quite as bulky. Don't let her size fool you: as a Primarch, she's far stronger and faster than any mortal Astartes. She's highly intelligent and perceptive, but woefully uneducated, a true Amazon warrior, fierce and relentless.

With access to the Primarch's genes, the gene-forges of the Dark Age of Technology was able to replicate the gene-seed of the Astartes to create the female equivalent of Astartes. Due to limitations in the female genome, these women Astartes are smaller and weaker than their male brethren but have 2 additional organs to compensate.