So was it that laying in wait in orbit of Jupiter, a massive saucer came to existence, esoteric technologies made it impossible for humanity's comparably primitive technology to ever find out about its existence. Inside it, the last 23'057 male Xeroz of the Yzvekan Hegemony waited patiently for the team of master geneticists to do their work on the human genome, developing the final version of the bioweapon intended to completely rewrite every humans biology into the one desired by the Xeroz.
The Xeroz were a alien species that humans would visually compare to the mythical centaur, a human with the lower body of a horse, though biologically the Xeroz had a most visible similarity to spiders, and of course, the horse. Their upper body were the most humanoid portion of their form, with thick bulging muscles -that to humans were only found on bodybuilders- that gave them a strength that far surpassed human limits, their strong hands had only 4 digits, 2 of which were thumbs, their skin was a deep purple with lime-green stripes, though more important members of their species could be other colours depending on their position, with crimson red (with glowing cyan stripes) belonging to royalty. The Xeroz head, unlike their human-like upper-body, was completely inhuman, being more akin to a cubic wedge atop a thick and squat neck with three pairs of sharp-yellow eyes with a strong, fanged jaw, strands of bony hair litter the back of their heads.
The Xeroz lower body is long and horselike without a tail, with 6 muscular legs instead of a horses 4 along the sides of the wide horse torso. The legs of a Xeroz though is more akin to a extremely muscular humans legs in terms of range-of-motion compared to the legs of a horse, their feet consisting of three digits meant for gripping onto rough, uneven terrain though could also serve as extra 'hands' to hold down their chosen mate. For mating, The Xeroz posess a universally neon-pink, 5-foot horse-like penis that can quickly retreat into a sheath with a ballsack containing 4 grapefruit sized balls. The Xeroz penis is notably ribbed and much thicker than traditional horsecocks, with blunt quills that fold out when the penis is being pulled back, and which secrete an slimy aphrodesiac that increases sensitivity in erogenous-zones its applied to.
The Xeroz came from their home system Zen, from their homeworld of Kax, on the verge of extinction as one of seven different expeditions with the goal of finding a new home and a solution to their problematic lack of females. This expedition was the latest of the seven, launched as a desperate play by their people before their society collapsed from strife and chaos following the death of the last Xeroz female. Communication through quantum entanglement with the other 6 expeditions had gradually been lost throughout the 7th's 43 year journey, 3 went silent due to technical problems, further fate unknown, with 2 others lost to hostile action from unknown powers, and the last going silent without any warning, like they'd either been instantly destroyed, or the connection was abruptly cut by something else. Either way, the Xeroz of the 7th expedition just 𝘬𝘯𝘦𝘸 they were alone.
Here, in Sol, the Xeroz planned to unleash a bioweapon upon humanity, having prepared for 15 years to turn Humanity into the salvation of Xero-kind. To do this, their bioweapon would be unleashed in atmosphere, and rapidly spread to every human on Earth, turning them into ideal forms for their objective of serving as the Xeroz wombs in their alien society. Afterwards, a second atmospheric bioweapon would be released, though this one would have the strict honour of killing off the first all without the humans nor anything else being affected. Then, when Earths atmosphere was devoid of any bioweapon, the Xeroz would first abduct every human outside of Earths atmosphere and directly convert them into humanity's new form and purpose, before the Xeroz mothership would decend on a small town in the US and abduct its entire populace while settling down and converting it into the first Xeroz city on Earth.
While this was going on, pre-deployed drones in orbit will activate and destroy humanity's entire nuclear arsenal and any site capable of producing the core of any nuclear bomb. Effectively eliminating both their strongest weapon and the only weapon capable of damaging the Xeroz mothership available to humanity.
And as the Xeroz expedition mothership silently coasted into the upper portion of Earths atmosphere, they unleashed their bioweapon responsible for genetically re-engineering the entire human race and prepared for the chaos their sudden appearance and first act would bring to the Earthen populace with stoic determination for the resurgence of their race.