You realize that 40k is largely a universe where such a 'spirit' can be lost can be lost, correct?

[...]

The only way I can see someone "becoming" untouchable is through some truly arcane, deeply traumatic and irreversible event that permanently cuts you off from the warp, ripping your soul away from you, leaving the dreadful husk behind.

A latent psyker is one who through some means 'bloomed' out into the warp, where once that spirit looked as a tiny human flicker, brightened into the beacon in the immaterium that is a psyker.

And so a latent untouchable would be the exact opposite, who was born with perhaps a tenuous spirit that eventually caved way into the nulling pit that is a pariah.

Those two obviously discount things like xenotech alterations.

Having your bones replaced by nullrods is quite a sensible 40k thing to do.

Even latent psykers are still technically psykers far before they manifest, and can be detected as such beforehand. The "soul" or "warp conduit" is already there; they just haven't realized it yet.

This is not actually true, and why many latents escape detection to become problems later. They are actually a normal human with zero ability to develop psychic powers before the trigger point.

In essence, a latent psyker likely cannot use psyker techniques at all, no matter how hard they try or if they are instructed in them, until they 'awaken'. (Which is described in the Inquisitor's Handbook, and perhaps elsewhere in the RPGs.)

There doesn't seem to be any lore reason this cannot be the case for an Untouchable.

I'm not sure why you're stating it would require anything more special than a nascent psyker style of trigger, or cause a 'dreadful husk' to be formed.

I mean, that's a bit like saying a nascent psyker will always rip a hole to the warp on awakening and get possessed.

Yes. I cannot see how you can ask me that after I said:

Because your post seemed to have two mutually exclusive statements in that regard.

If you're agreeing that a 'spirit' can be lost to become a null, the first part of your post would likely be inaccurate.

As a 'spirit' can be lost, and psychic nulls are usually created genetically, it would seem that a mutation or potential alteration in genetic transcription due to external stressors may be able to do it, among other potentials.

It probably comes down to interpretation and preferences, as with most things 40k. The fluff in GW's Inquisitor game does exclusively mention it as "an affliction suffered by only a handful of children across the galaxy in each generation", which somewhat goes against the idea that it could naturally develop later in life.

Like most outsourced material, however, Dark Heresy has always had its own ideas on stuff, simply because it's different people working on the product and the absence of consistency requirements when it comes to such minutiae.

Another example that always bugged me was the "Denounced and Condemned" background package for Sororitas - because of course the Schola Progenium as an institution of the purity-focused Ecclesiarchy would never tests its orphans for the psyker gene, and because of course an organisation as fanatical as the Sisterhood would never simply transfer one such embarrassment into the Repentia to find salvation in honourable death, or just execute her outright, because "just letting people go" is totally a 40k grimdark thing to do, right?

/rant

Another example that always bugged me was the "Denounced and Condemned" background package for Sororitas - because of course the Schola Progenium as an institution of the purity-focused Ecclesiarchy would never tests its orphans for the psyker gene, and because of course an organisation as fanatical as the Sisterhood would never simply transfer one such embarrassment into the Repentia to find salvation in honourable death, or just execute her outright, because "just letting people go" is totally a 40k grimdark thing to do, right?

/rant

"Denounced and Condemned" states that the Sister was imprisoned and tortured for being a witch, and that she is not actually a psyker.

Only the inquisitor's authority saved her from what would apparently have been near continuous questioning and torture to determine if and how she consorted with 'dark powers' until she died. (Presumably why they didn't kill her immediately.)

Although she is still 'condemned as a heretic', and perhaps not permitted any dealings with her former sisters, not even as a Repentia.

For the screening, the Imperium may be incapable of large scale genetic screening for the psyker gene (or genes), and may not be much aware of what specifically causes it. That understanding is probably still along the lines of the archaeotech level that created the Navigators. Presumably they use good old fashioned witchtests and tons of psyniscience for most cases.

Genetic testing would additionally be the realm of the Adeptus Mechanicus Genetors and Magos Biologi, and those studying the psyker gene may even be 'techsorcists'-- they may or may not be inclined to work with the Ecchlesiarchy, perhaps for fear of being branded heretics themselves.

For the screening, the Imperium may be incapable of large scale genetic screening for the psyker gene (or genes), and may not be much aware of what specifically causes it. That understanding is probably still along the lines of the archaeotech level that created the Navigators. Presumably they use good old fashioned witchtests and tons of psyniscience for most cases.

Genetic testing would additionally be the realm of the Adeptus Mechanicus Genetors and Magos Biologi, and those studying the psyker gene may even be 'techsorcists'-- they may or may not be inclined to work with the Ecchlesiarchy, perhaps for fear of being branded heretics themselves.

Purity checks like these is how the Imperium collects the psyker tithe via the Black Ship fleet - it'd only be even easier in the centralised Schola Progenium facilities where every single pupil is subject to stringent evaluation. The Imperium also has devices such as psi-trackers capable of gauging the psychic potential of an individual (although it could be argued that these are rare items not commonly found outside the Inquisition). But the Sisterhood in particular is, in addition to its other duties, also charged with hunting down rogue psykers as part of its Ecclesiarchal mandate. And last but not least, the Inquisitor rules for Inquisitor were very explicit in ruling out psykers within the Ministorum or the Sororitas.

It's just one of the small details where this game deviates a bit. There are many, many more. In each of the games that have been released so far. Some people don't mind, others would prefer consistency. For me, it's probably just even more annoying because it also concerns one of my favourite factions, so I am doubly biased here.

in the RH background package the Inquisition just "appears" out of nowhere to steal a Sister who apparently was about to be put to death away.

It's certainly possible that the writer(s) had some idea to explain how this all worked out in detail, but if so, it isn't hinted at in the background at all, which is a bit problematic.

This is deliberate, and happens in almost every background package.

As an RPG, it is up to the players to decide for their own characters how they came to the Holy Ordos.

Conversely, if this background package is closer to BoM Sisters and their "space magic" version of Faith, then it is quite possible that Witch Sight is supposed to represent some sort of divinely granted ability, but in this case it would become problematic to explain why an organisation whose members are used to seeing their fellow Sisters cast friggin' rays of light out of their eyes suddenly goes "SHE'S A WITCH" because of something that's not really any more unnatural than that.

Now now, Sororitas have always had space magic.

To more or less extent, their whole thing is 'battle miracles', from Celestine to ignoring cover.

As the talent goes, "Witch Sight" is close to mindreading, rather than purging daemons with golden light and the extra-specialness of 'Fate Points'.

That mindreading might even be an Emperor-sourced boon, like the Emperor's Tarot, although the superstitious Ecchlesiarchy certainly might not consider it that way.

(After all, they perhaps wouldn't even like the Emperor's own Imperial Truth from his very mouth. AKA "Don't worship me newbies, go for innovation and human solidarity!")

Purity checks like these is how the Imperium collects the psyker tithe via the Black Ship fleet - it'd only be even easier in the centralised Schola Progenium facilities where every single pupil is subject to stringent evaluation.

Yes, they're very good at detecting active psykers. (Albeit perhaps through usually non-genetic means.)

Latent psykers often escape detection, and the process isn't flawless.

Even the Black Templars miss psykers before they receive the gene-seed. So they may send them off to the Deathwatch.

But psyker detection may not detect those with non-psyker abilities, like 'gifts' from The Emperor.

That's the sad irony of this background. "Witch Sight" probably is a boon direct from The Emperor, complete with the 'fate point' activation cost-- but her sisters' superstition alone commits the poor young girl to torture and death.

As an RPG, it is up to the players to decide for their own characters how they came to the Holy Ordos.

A background also should provide some pointers as to how it even became possible for the character to survive something, though. I could see a lot of players not even noticing the potential issues here until they are confronted with them and have to make something up on the spot - which is always a bit awkward. Ideally, a GM should guide them through this process at chargen, but ideal doesn't mean it always happens.

Now now, Sororitas have always had space magic.

Not in GW's version of the setting* - which is what I "grew up" with, and which is why I absolutely dislike Blood of Martyrs for having pushed it so far beyond the usual ambiguous nature of Acts of Faith. In my opinion, it makes the Sisters less awesome, and it makes the Emperor too special as the one being in the entire setting that apparently has the monopoly on D&D-style divine magic (and simultaneously making the Ecclesiarchy actually be right rather than just following silly superstition) whereas everyone else just gets Warp sorcery. That's just, like, ultra-lame, and lets Space Marine unbelievers look like fools.

I want mah grimdark back!

(*: if you're interested, I can provide several sourcebook quotes on that subject either here or via PM - but then again this is not really a part of this debate)

Yes, they're very good at detecting active psykers. (Albeit perhaps through usually non-genetic means.)

Latent psykers often escape detection, and the process isn't flawless.

As per Inquisitor , they can also detect latent psykers - an example being the Daemonhunter Umberco Eto (yeah yeah @ name ) who was a young gunrunner on a Rogue Trader vessel that was boarded by an Inquisitorial ship, with the entire crew being subjected to psychic testing.

Psychic potential, just as the condition of Untouchables and Pariahs, is genetic in nature and part of human evolution (one of the big grimdark themes in the setting - the Imperium desperately trying to halt nature's progress because of fear), and as such it can be detected by obtaining samples, much like the Inquisition and the Sisterhood test the Imperium's populace and armed forces for other mutations.

The same goes for the Navis Nobilite, who are so dependent on genetics that their lines would lose the ability to "see" the Warp if they would have offspring with someone outside the Navigator Houses.

Is the process flawless? *shrug* Apparently flawless enough that GW saw fit to issue a blanket psyker ban on Ecclesiarchy and SoB characters in their game.

Now, if "Witch Sight" truly is a divine power, the above concern is simply replaced by my lack of understanding for an organisation used to all manner of weird, crazy magicks displayed by its members, yet throwing a hissy fit as soon as you have a girl who claims she can see evil people just by looking at them. And again, one of the Sisterhood's most sacred relics works exactly like that.

And, as mentioned before, Sororitas just not "working like that" in the original material.