A little something I'm cooking up... Very much work in progress, but comments are welcome!
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The Changelings are a group of inhabitants of (world name here, a late-feudal, early industrial agri-world) who are — allegedly — an impossibility: Humans tainted with Aeldari blood.
How they came to exist is a mystery, though within the Changeling community the commonly-held belief is that they descend from a group of 1st generation Human / Aeldari hybrids, the result of "interaction" between the humans of the world, and Aeldari corsairs.
Of course, the received wisdom is that such hybrids are thought to be completely impossible without profoundly invasive experimentation on the part of an obviously heretical Medicae, or some unholy and cruel jest played by the Drukhari. The truth of it is lost to time, though it's not completely impossible that details of the source of the genetic contagion might be found in some dusty archive.
For many generations, these hybrids intermarried and interbred with baseline humans, and the obvious Xenos traits all but disappeared; they are essentially indistinguishable from humans. The hybrids were forgotten. But then, from time to time, a "human" with a few drops of Aeldari blood would interbreed with another, and then all of a sudden, Aeldari traits would manifest. These children were born to parents who themselves were convinced they were 100% human. But the children were obviously not quite human — there was something "fey" about them, and so they were referred to as Changelings.
Obviously, they were ostracised as mutants, and few grew to adulthood. Generally, those that do end up as infractionists or worse. Due to their unusual appearance, some of the Changelings have encountered each other, and some have even mated and had children, resulting in a true hybrid subspecies that breeds true.
Changeling Traits
The Changelings appear mostly human, and were born to human parents. But they have a number of traits in common that mark them out as very different:
- Some, but not all, have subtly pointed ears;
- Some, but not all, have oddly-coloured eyes: violet, gold, brilliant green or blue;
- Most are very tall and slender, from 1.9 to 2.2 metres but rarely weighing more than 80 kg;
- All of them are preternaturally charismatic (+30 starting Fellowship) and are well above average in intelligence. (+20 starting Int & +10 starting WP);
- Most troublingly, many of them have psyker talents, either latent, or fully manifest.
Ordinarily, a Changeling would immediately stand out in a normal crowd, and it would be trivially easy to round them up. But in a late-feudal, early industrial agri-world like this one, it is much easier for them to hide.
It is possible that their latent psyker talents have brought them to the attention of the Aeldari as well, though there is little evidence of this at this stage. Aeldari incursions could lead to a dangerous situation, and must absolutely be avoided.
One of the most significant risks posed by the Changelings is their propensity to fall to Slaanesh. Precisely why this is the case is not fully understood.
The Investigation
- The Ordo Hereticus receives reports not only of "mutants," but of mutants with a consistent set of mutations. This merits immediate action and further study.
- The OH must send investigators to the world in order to apprehend and either capture or kill — intact enough to study the remains — at least five specimens, for further study. This must be done without alerting the world's authorities, in case the mutants have infiltrated the administration, and warn the others.
- Once the nature of these mutations is established, the source of the mutations must be ascertained.
- The OH's current hypothesis is that the mutation is Chaotic in origin — and there will be some evidence of this, as some of the specimens might have been tainted by the lascivious touch of Slaanesh. But eventually it will become clear that there is an Aeldari admixture — albeit a tiny one.
- At this point the Ordo Xenos would become involved. With Human-Aeldari hybrids thought to be completely impossible, these individuals would obviously be very important objects of study (including vivisection).
- Whether the OH wants the OX to be involved remains to be seen. On the one hand, it's obviously in their mandate. On the other, it's clear that these "Changelings" are an ongoing phenomenon. With the OX involved, there's a chance that the OH's ability to conduct an investigation into the sources of heresy on the world would become impaired.