The daemon’s appearance is, if anything, more distracting than it would be on Earth, or any successor civilization thereof. Dath Ilani go around with face blinders to limit the stimuli caused by some appearances, and are very vulnerable to the hedonistic treadmill. Still, the idea that aliens would try and appear pleasant to them was in fact very obvious, and some steps were taken to mitigate the effects. People in first contact select somewhat for being less effected by this, and have been exposed to significantly higher steps on this ladder than your standard dath ilani. To aid further, they are trained in a variety of keeper techniques, which were recently augmented by additional training in the last week. At the point they stopped, it was predicted that increasing the estimated effectiveness of their efforts by 20% would require 5 times the budget. 

Dath ilan would dismiss the suggestion that this constitutes actual security, but to someone expecting the imperium, this is like heading to a fence gate and discovering a solid door with a padlock and deadbolt. A daemon can break such a door pretty easily if they tried, but if you give it a halfhearted kick expecting the whole structure to come falling down it might be mildly embarrassing.

This about daemonettes: They are, by their nature, very perceptive, and have an innate ability to read the deep hidden desires of anyone around them, as well as enough innate telepathy to speak and understand what they are told without actually knowing the language in which they are told it.

Yslivianne immediately notices that the room she's in is nothing like what you'd usually expect from the humans: no visible technological contraptions, no dirt or mold AT ALL, no gold or steel, no skulls, no posh inscriptions in High Gothic or grafitti in Low Gothic... No visible weapons anywhere either.

When she feels out the secret desires of people around, she becomes increasingly confused. These people want weird and convoluted and almost non-humanlike things! In fact, all they think and say is full of weird convoluted almost non-humanlike things!

When this priest guy have said "Civilization" and "Light", a torrent of unfamiliar concepts and numbers materialized in Yslivianne's head through telepathy - instinctively graspable, but way too much to untangle. His other words are simpler, but still terribly convoluted. These people's desires and language make her head hurt.

Normally, it's the Daemonettes who torture people through excessive intricacy!

(That "Light" thing actually sounds vaguely Slaaneshi! That should be interesting, but Yslivianne is kinda overwhelmed.)

By the way, none of the annoying presence of Anathema anywhere - neither in the place nor in anyone's minds. A relief, but...

It's becoming clear that these people have nothing to do with the humanity as Yslivianne knows it. From a strategic standpoint, this is an excellent reason to slow down, go with the flow, and try to orient.

This about daemonettes: They are MADE OF HORNY. Quite literally. They are VERY VERY HORNY, and that is their default state and, usually, dominant emotion. Thirst is their life. 

Of course, they are capable of doing a whole host of things other than acting on their horniness. Within their vast ranks, there are gardeners, sculptors, soldiers, deep-cover infiltrators, therapists (being written as one word isn't a typo), and even genuine diplomats specifically trained in such complicated skills as "not seducing or corrupting people who you are trying to negotiate with".

But even then, HORNY is still their fundamental nature. 

This daemonette is not from any of the categories listed, and moreover, in the overall confusion, she is falling back to that default state, that fundamental nature. Strategy? Yeah, about that...

Other people are thinking her looks and aura are... really distracting? Not distracting enough, if you ask her! These people should get more distracted, fast!

The daemon (technically still just a possessed mutated human) yawns seductively, and whispers, as she finishes stretching:

"In the name of Slaanesh, the Prince of Pleasure, greetings on behalf of Chaos, my dear. Now, come closer, will you? I want to explain what that means in more detail..."

(The words are kind of a mental assault. Everyone present now feels a desperate sexual desire towards Yslivianne, and everyone without full control over their reflexes is instinctively drawn forward by unconscious motions of their legs.)

Yeah, that's gonna go through.

Sexual contact is not the most likely form for alien communication to take. It's not even in the top 3. But it's very simple, conceptually speaking, especially when considered alongside the broader category of  "positive sum coordination paired with positive sensorium." Even dath ilan, who takes great deontological care to not engage in social actions analogous to politeness, wouldn't ask aliens to do diplomacy in uncomfortable chairs or rooms to conduct diplomacy if they could help it. Aside from the potential to interfere with coming to mutually beneficial agreements, it would just be plain embarrassing to fail that badly.

Much of the hiring preparations took the form of hiring really good computer programmers, linguists, cryptographers and mathematicians, as well as engineers to rapidly produce anything that became suddenly needed. But some of them went to preparing for this sort of possibility, and at their core is a group of keeper sex workers with smaller (and varied) disgust windows from the typical dath ilani, as well as the ability to modify themselves further. They have extensive training in biology, speculative xenobiology, dexterity, and dozens of other skills designed to be able to facilitate communications of this sort as needed. To support them is a broader crowd of dath ilani with more specific divergent tastes or general acceptances that it was inconvenient to source in numbers from only the population of keepers. It was their services dath ilan was primarily advertising in its prior broadcasts offering sex. They are also, of course, very good at almost every kind of sex actually practiced by dath ilani.

Jacem is not one of those specialists, and neither is his companion. However, he is still a keeper and a member of a first contact team, which involves a certain baseline level of competence. Also helpful, of course, is that the daemonette is roughly human in appearance, and an exceptionally pretty one at that. He still has some control over himself, but even on reflection this wouldn't necessarily be the wrong course of action in a general first contact situation, and with her economicmagic attraction strengthening his libido and weakening his self reflection (and the meta self reflection to correct it), he complies, and notices his companion does as well.

Security, on the other hand, is a ways off, viewing the entire scene through a filter and strongly selected for self control even among keepers. They still feel the effect, but in a way that triggers their internal alarm scripts, and they press a button to alert exception handling. 3 keep their full focus on the situation, while the fourth makes a longer report; they'll swap out, one at a time, to do the same.

They don't pull the trigger, though, not even on nonlethal attacks. Survival mode or not, mental effect or not, mysterious circumstances or not, dath ilan really doesn't want to be the one to initiate conflict in a first contact scenario, nor to be the kind of entity there's any doubt about your ability to approach in good faith. Not being idiots, however, the other first contact attempts are paused, the base moved to a higher level of lockdown, and a prediction market on how to deal with contact turning fully hostile gains liquidity.

Hey, the strategy of being aggressively horny at people worked, as it always have in the past! There's no reason not to continue doing that!

This planet will make such a pretty Daemon World!

The people dragged in experience the best sex in their life, by far. They also experience runes of Slaanesh being drawn on them, and hear utterly blissful singing, and absolutely caressing whispers. They experience a presence of some Huge being - a being very pleased with their efforts around running the henodic treadmills, but very eager for them to go further, and further still. Somehow, it feels like a good idea to revere it, like the people of Old revered their false idols. These people are gonna have interesting dreams in the future, and maybe some interesting mutations.

But, of course... pure pleasure is good, very good, don't get Yslivianne wrong, but it's kinda sickly sweet - as most other daemonettes would readily agree. It's gotta have that element of suffering, to balance the flavor. And maybe some artistically satisfying death in the end.

So, at some point, without bothering to ask, she starts to spice up the experience, at the expense of one of them, at first. To the people involved in this act, in the heat of the moment, it will somehow seem like a good idea.

Pained screams mix in with the moans.

In a badly designed system, this would be where you throw an exception. Badly designed by dath ilani systems, that is; if this were a project run by the imperium, it would never have gotten this far without failing catastrophically along lines dath ilan values even if it decided to try and save them in the first place, but if by some miracle it had not, this would be when you flipped a coin between security standing around doing nothing and opening fire with their guns. 

In the actual project, there is no need for either. The security themselves are both qualified for their actual jobs and for exception handling, and because dath ilan believes in actually succeeding at difficult tasks there is a line of exception handling for them anyway. Expert advice and experts are tabulated and come to the conclusion that there is still enough probability mass on this not being intended as an attack on civilization to be worth preserving when weighed against worldlines in which that hypothesis is accurate. With references to the prediction markets, they determine the most value preserving option is to send in a specialized team of first contact sex workers, with additional selection criteria of being skilled at dealing with human bodies, masochism or pain ambivalence, and ability to focus and communicate during periods of high sensory input, to distract the alien and attempt to advance the first contact scenario along dath ilan’s intended lines. Meanwhile, another team with sensory blockers, no headache susceptibility, and good self control are sent to retrieve Jacem and his fellow, for treatment, recovery, and ideally debrief. The expected success rate for this maneuver is hovering at about 70%, based on how the alien seemed to react to Jacem employing their own more limited arsenal and their rate of adapting to different stimulations; conditional on it failing, it is also expected (60%) to allow for a significantly more precise gauging of Yslivianne‘s intentions and plausibly (45%) not seriously cost them in negotiations. Armed security will enter the room with them equipped with non lethal weaponry, to guard against the negative tail of the outcomes bell curve. They have lethal force ready and available, but even if it turns hostile nonlethal is judged more value preserving if feasible.

3 such sex workers is judged to be the ideal tradeoff point between increased odds of success and costs of failure, when accounting for the diminishing marginal utility. They bring with them sex toys, specialized cuddleroom cushions, and a handful of other quality of life advantages dath ilan considers standard.

It’s unlikely to be a new situation for someone to try and distract a daemonette like this. Less likely to be typical is for them to be actually good at it, even beyond the relatively impressive repertoire used by Jacem, nor for them to have equipment worthy of the name. Outside of Slaaneshi and Dark Eldar, it’s quite rare for any society  to even consider this a domain you can try to be societally good at, much less put effort into actually succeeding; among those civilizations that do not demonize sec work, there is a disturbing lack of engineering know-how and effort spent on optimization of the experience. 

In comparison, the team here to retrieve Jacem and his cohort are much easier to miss!

Uhh. These people sure don't know what they want, do they? Are we fighting, or are we being willingly corrupted? Or... do I get to choose?

Obviously, I'm choosing corrupting the willing! I'm not some Khornate brickhead! I'll trade weirdo nerds for "sex workers" any day!

And hey, these "sex workers" are already almost there! Just a slight push here... a light touch there... a few good old Chaos runes... and here we have it! These people are now thoroughly playthings of Slaanesh, as is good and proper! That has to be celebrated!

Yslivianne kisses one of the "sex workers" deeply, and her soul departs into the Dark Prince's Realm, to experience interesting mindstates for the rest of eternity (?). The other two start to enthusiastically tear her apart, with the intention of feasting on her meat, which Yslivianne will also join.

I mean, these three people obviously came here for some good ol' debauchery. They brought torture toys and everything!

It wouldn't make any sense to get upset by a little mutilation now, would it? Hell, no one have even reprimanded me for eating the summoner!

Yeah, no.

Subtlety is abandoned. A magnetic grapple is fired at the sex workers, clipping onto a matching magnet on their back  and dragging them away. The rescue of the original contactees doesn’t have quite the same elegance, but they’re also not surrounded. Both attempts have the potential to cause some injuries, but leaving them there will cause more and also likely other negative effects. Simultaneously, a net covers Yslivianne and then magnetically locks against the floor, before tightening to reduce the room to struggle. They have tazers and gas, but there’s no need to take risks with electricity or potentially do experimental xenobiochemistry on the spot if kinetic force and mechanical engineering will do the trick. The net is made of woven strands of carbon fiber and armored against cutting by a layer of titanium alloy, and are immediately followed up with by further restraints. 

An observer might call the timing and aim of the shots inhuman, but a dath ilan would tell them they could do it too, if they tried hard enough. It’s not like it’s that hard to redevelop the athletic principles and engineering required from a standing start, after all.

The exits to the outside world have been thoroughly sealed for a while now, but once the non security personell are evacuated to a section of the cordoned off area for emergency treatment, that section will seal off too. 

The security are chose for their competance, experience dealing with info hazards, mental discipline, and lack of any headaches or other mental economagic responses. These requirements are rated at dath ilan’s standards, but even then when considering keepers that’s still a much larger recruitment population than you might think.

Even among this group, armed as they are with equipment designed to limit their inflow of sensory data and keeping their distance, they aren’t unaffected by the aura, just able to work through it. It’s this very downside, however, that reveals a useful - if worrying - data point. As long as they are in combat, the strength of the attraction diminishes; not a lot, but noticable, when you track your mental state as much as keepers do. Dath ilani are not idiots and do not uncritically accepting of this as true, much less a positive, but it’s added to their models and as an emergency measure, to be tested when a safer way is found at a future date. The effect is lesser, but still noticeable now that they know what to look for, when they go from direct combat to ready position with an eye out for responses.

“Dath ilan does not appreciate harm to our diplomats, nor mental interference with the execution of our duties. Cease, and this need not get worse for you.”

AHHHHH WHY YOU BROUGHT TORTURE TOYS AND EVERYTHING

Screw it. She've had a good time, she have thoroughly doomed this warp-naive planet, these people are CONFUSING and this net is HOLDING HER and THE SEX IS OVER and you know what?

Her work here is done. Done, she says!

"Yeah, I really don't get you guys. You do whatever. Maybe that Light thing'll be good for ya. Toodles!"

And Yslivianne leaves for Warp, as her body dissolves into an organic mess.

This could have been worse. Nobody says that, of course, even though in dath ilan that particular story trope is far less common, but the thought is there. There is a reason most alien invasion rehearsals aren’t reslistic, and it’s that they’re too depressing. Sure, this was in some regards an almost ideal situation, with only one alien coming into a location already under surveillance by armed keepers, but for some possible aliens - especially economicmagic aliens - that would be enough to destroy dath ilan. That’s not to take away from the tragic loss of at least two and possibly as many as 4 lives, but it was a risk they knew they were taking just by attempting this. Some heads will roll on the markets that’s in retrospect, somewhat underrated the danger, but with the numbers they had to work with the plan was reasonable even in the post mortem.

The victims, once it is determined they are unlikely to make any kind of recovery and have no useful tactical information they are able to convey (in dath ilan with keepers, this is a very swift process indeed, especially considering the state they’re in) they are prepped from onsite cryogenics. They’re significantly less confident than usual that they will be able to wake them up in the future, but unbounded artificial intelligence and economicmagic are both unknown unknowns when it comes to capabilities. It’s not pointless, not like the former person now forming a twisted ball of ex-flesh under the net.

Of course, just because it seems over doesn’t mean they come out of lockdown or the base goes off alert, just that they undergo screening questions to assess the effect of the mental attack and exhaustively record their experiences and impressions for analysis. Others within the cordoned off region set up the instruments for remote examination of the remains of the person, in case there is anything to be learned from it without getting any closer. Everyone who entered the room undergoes a thorough decontamination to cover the relatively long odds there is material cause, and everyone even near it is to undergo thorough surveillance during the waiting period. The reports will undergo infohazard screening by an entirely unrelated group of keepers before a limited dissemination occurs.

Across dath ilan, an advisory of potentially hostile aliens is put out. Dath ilan’s population can be expected to react reliably intelligently to that, as well as details of how to detect their intrusion or mitigate the effects. The specific methodology employed in the effort to reach out that cumulated in this is also banned, covered incidentally in a set of broader rules on economagic experimentation that happens to include this and a few other strategies with plausibly similar results. It’s not that they expect sharing how they did it would lead to a copycat among their population in a less secured area, but why trust what you can cheaply verify? Devices are prototyped with the aim of detecting the physiological changes associated with the mental effect; both false positives and negatives are epxlexted, especially considering their theories on other categories of mental influence, but they will be noticeably better than nothing when used intelligently and centrally tracked. Militarily, dath ilan is already on alert and there are serious costs to increasing readiness too much higher for too long, but preparations are made for responding to potential incursions or arrival via an alternate method of more aliens similar to the one they encountered. Training of citizens in those keeper techniques that proved most effective is prioritized, especially those in the military, governance, exception handling, and logistics. Surveillance of everyone who experienced headaches continues, with a somewhat different list of things to primarily look out for.

Well, with the echoes of the call dispersing relatively far in Warp, and a survivor returning to tell the tale, the Immaterium around dath ilan is soon going to get filled with a lot of daemons of all four kins lusting for it and spying on it and seeping into the dreams and fantasies of people. Eventually, it's location is going to make it to the Chaos Space Marine legions, Chaos cults in the Imperium and Chaos sorcerors, and from there, to who knows where.

Though recognized as weird and curious, the sheer importance of this world is largely lost on the daemons, except for the Greater Daemons of Tzeentch, who, being made of planning, aren't babblemouths.

This about the daemons of Tzeentch: They come in two categories. The first one are the lesser demons - who embody the more direct and physical aspects of Change and Pursuit. Though great at throwing combat magic around and turning things into different things, as well as being utilized as power sources and tools, they are barely stable, obsessed, insane, and rather freaking dumb. Not someone you'd want to trust negotiations to.

The greater daemons and daemon princes of Tzeentch, meanwhile, embody the mental side of Tzeentch, the conscious organization of Change through Knowledge. If the minor demons are insane fools, the greater daemons and daemon princes are insane geniuses. And their insanity is always uncontrollably contagious.

For that is how most of the Galaxy percieves - and uses - knowledge.

Which, of course, means that the greater Tzeentchian deamons are also terrible diplomats when sent towards unprepared people.

(And Tzeentch himself is a perfect diplomat, of course, but he can't just go manifest in realspace willy-nilly!)

Usually, genuine negotiations of his faction with unprepared people would be conducted by his sorcerors.

What a lucky, lucky coincidence it was, that there weren't any Tzeentchian daemons around during the first contact. The God of Planning cannot just go ahead and leave such a terrible first impression on those wonderful, wonderful newcomers.

And if the forces of Slaanesh, the God second most aligned to dath ilan, get to embarass themselves... well that's just so unfortunate.

There may eventually come a moment where the Father of Lies and Deception will need to lay his mind bare before the very clever people of dath ilan. Tzeentch considers erasing this plot from His memory - as would be trivial for the Lord of Change - but decides against it. This wasn't much of a transgression, and He cannot adopt this sort of deception as a policy - those with excellent grasp of probability would piece it together.

He'll be patient. He is patience himself.

And when the time comes, He will welcome His wayward children with open arms...

The information of the new planet seeps to other Gods, and, though they only expend miniscule amounts of attention on it, they have their reactions.