So I was looking at S@20 again recently, and I saw that both Xayah and Zoe have brief descriptions of their lore that actually reveal some very interesting things!
"Many years ago, Xayah was destroyed in the fight against Zoe, alongside her lover Rakan. The pair were then resurrected and turned against their allies -- a change Xayah seems almost happy about. Blaming the Star Guardians for abandoning her to die, she has taken a bitter, personal stand against them, even as doubts begin to creep in..."
"A member of the ancient, first group of Star Guardians, Zoe’s heart desired not love, but chaos -- twisting her newfound power into a malignant expression of cosmic madness. After numberless eons of hunting the First Star’s chosen, she has finally come to Valoran City, hoping to destroy the latest generation of Guardians as she has countless others."
I'm not sure if these are their official skin bios, but the way they're worded seems to hint towards it.
Rakan and Neeko also have short lore blurbs, but they don't reveal much at all except the very basics.
"Star Guardian Rakan is here to bring darkness to the Universe. And get some new hair gel!"
"Star Guardian Neeko has descended from the stars to come to the Star Guardians aid! Will she be able to defeat the likes of Star Guardian Zoe?"
I may edit if more lore is added or changed in the PBE. Feel free to start theorizing...
***EDIT:*** Rakan's and Neeko's official bios have been added to the PBE!
"Many years ago, Rakan was destroyed in the fight against Zoe, alongside his lover Xayah. The pair were then resurrected and turned against their allies -- a fact Rakan seems keenly aware of. Biding his time to strike, he has a plan to purify the darkness from Xayah's heart... though the price may be losing himself to evil forever."
"A member of Miss Fortune's original team of Star Guardians, Neeko watched her teammates fall against Zoe's dark powers, going into hiding when she, too, was thought dead. Revealing herself to the newly assembled Star Guardians at the eve of their greatest battle, the wide-eyed adventurer has vowed that this time, she won't run."