One starry night, as the suburb in washington state slumbered, a craft streaked across the sky, the unknown visitors landed their craft in an empty field to take samples of the flora, scan the surroundings, and take long rang scans of nearby humans. The scans they took led them to unsettling comclusions about this middling civilization, inadequate medicine was holding back and otherwise civilized species and hardship was keeping them at eachother's throats. These alien visitors had medical technology that could fix this, and even offer those with various dysphorias and desires for their body a way to become their true selves.
The aliens went into their craft and slid a vial of isolated nanites into a chamber of media to multiply them, they would need billions of doses to inoculate the planet as they had so many before, granting salvation to every world they found, making plans to terraform all the planets in the solar system that had sufficient mass to support an atmosphere.
These visitors began by disguising themselves as humans, holography being one of their more advanced technologies, then used a set of nanites to build a research building that looked human-constructed. They used their communication devices to plant ads for their new "clinic" at the end user side of media viewing, to hide their pirate beoadcasts from humans with means. They advertised exactly what the individual user needed for every user separately, even offering gender affirming care that was discreet. A small group of humans arrived for the treatment at first. The treatment consisted of an injection of nanites that gradually broke down and replaced cells and DNA with an optimum form of itself, reversing and halting aging at senescence, repairing any and all damage, destroying cancer, and even giving them a body they desired.
The first group of humans got the nanites, whose work was so subtle they didnt realize it was happening until its work was nearly complete, the humans attained their idea of perfect beauty for themselves, in some case in unorthodox ways. One human took the nanites and began turning biologically female, the visitors marked that as expected, but then she began to grow fur, and then a snout began to grow, muscular tissue began to generate en masse and her appetite increased dramatically. In a month she had become some mix of earth canine and humanoid, the visitors marked that as a sign if incompstibility until they noted that this made her extremely happy, they marked it as an abberation and decided to watch for more.
More abberations occured, many of their treated humans became part animal, or in some cases fully feral animals. Some of them even appeared to become fictional creatures, like dragons or pokemon whuch they scraped the internet for intel on. Then they discovered the furry community, and suddenly what they saw made sense. "These defective humans... They are not defective after all! This is reminiscent of what occured on Gardnen III wherein some of the beings there desired to stay in larval stage!" One visitor said to his captain. The captain oversaw the work and nodded before remarking "good, we want to help these people become their greatest form." Her words were compassionate, but an ill feeling welled inside her as she feared one of these humans may desire to become something dangerous.
The town was almost all treated when a suspicious human entered the clinic, a dark look in his blue eyes, the look of a killer. The human had dark circles under his eyes and lomg dark hair, a wide build, and a combative stance. Despite these things he clearly attempted to act friendly, their brain scans saw that he had chronic pain, and other permanent health conditions, he was riddled with pain. The visitors gave him the nanites as they could tell the pain was wearing on his nerves in ways he couldnt describe.
Moments after the injection his skin began turning black, inky black tentacles sprouted from the black spots and he began to mutate into a black, betentacled humanoid monster. The visitors attempted to turn off the nanites but he had already directed them to develop signal blocking countermeasures, he knew they were trying to turn them off, he could smell their intent now, and he disabled the visitors without killing them, breaking out of the facility and escaping their weapons-fire.
The visitors shuttered the program immediately after intercepting news broadcasts of a mysterious infection soreading across the country, turning people into monsters, animals, robots and worse, and these creatures marching to destroy their government. The visitors immediate took their leave of earth. "What have we done...?" The captain asked rhetorically as news broadcasts came in about a new species of intelligent life conquering the planet.
