Can you teleport outside? Sure.
Is it safe? So long as there's no rain to smudge your diagram it's basically as safe as doing it indoors. And in Lucien's defense there wasn't any rain at all, right up until the last sylabble of the incantation.
None of his wards are pinged which eliminates a bunch of the known options. The magic sensitive ink dot he painted on his hand has gone completely black so this guy is definitely something pretty powerful. Tail and wings pull in an obvious direction but the blue skin points otherwise.... and distracting abs which indicates some sort of mental effect so, most likely option...
Lucien pulls a glass vial of holy water out of one of his jacket pockets and hurls it at the possible-incubus.
"Ah "
.... This feels terribly impolite but he literally just said he was a demon so Lucien is going to ignore his feelings and start uncapping and throwing additional vials, in case quick silver, garlic infused oil, virgin blood, or hydrochloric acid seem to have any effect.
When he gets to the hydrochloric acid somebody emerges from a side hallway, rushes him too fast to track with the eye, seizes it from his hand and flings it behind the bar where it vanishes, and whisks him into a room down that same hallway where she sticks him in a forcefield-barred cell.
....Was that there before? Probably. Lucien was rather distracted by the demon.
He... has no further guesses as to what is going on. Which means his brain has been very very badly messed with - so badly he can't notice any sign of it - or this is genuinely something completely unexpected. The latter is basically useless to reason about, so he'll assume the former.
"Uh, I'm sorry for throwing all those vials at you. I was not aware there were safe alternatives."
"It does lots of things. Uh, perhaps you could go on in any more detail about the demon situation in your universe and why you felt throwing things at me was an appropriate response to that situation, so I can calibrate at all before attempting to give you a tech uplift."
"Largely priors - very few magical entities I've encountered have been safe and even fewer have been well intentioned. I've never actually met a demon in my universe and was not confident they existed, but the myths surrounding them feature quite a lot of torture and fire and I'd strongly expect the reality to be at least as bad as the myth."
"I don't actually know how much the geopolitics turn on specific dudes and you probably want to at least read some books to both confirm that the dudes suck and that you don't have a better lever. Maybe you're actually in a great position to create a Jewish ethnostate somewhere in Canada and get industrial technology accelerated so fast that Communism doesn't kill a ton of people. It's just, you know, for the next couple hundred years every conversation about time travel inevitably derails on 'but of course you've got to kill Hitler, first thing', so it popped into my head."
"I could plausibly set-up a small Jewish ethnostate somewhere if I dropped everything else - though I doubt I could get it stable enough to survive people finding out I'm a sorcerer so it's not very viable. There's a famine in the Soviet Union right now that I think an industrial revolution is too late to fix. Also wait did you say next couple hundred years."
Does he want a textbook on summoning? Here's one of those. Any kind of daeva can kill you, of course, if they're not properly bound. Bindings prevent fairies from decapitating you and angels from turning you into goo and demons from interpolating you with air. The more serious risk is actually that they won't kill you, and will instead incapacitate you alive and go run amok - if they kill you, they go home. Fairies are less dangerous in this respect in particular especially if you have a state of the art chiplock.
Which means this is probably the safest place to talk to a demon.
Lucien scans through the literature on medical advances again, taking notes. And then it's time to go and talk to the demon, again.
"I'm sorry to bother you again but I was wondering if I could trade with you for some items."
Lucien has a list of future medical tech, mostly for reverse engineering purposes though some items are feasible to make and transport from here in large enough quantities on their own (like some vaccines, so long as they come with refrigeration units).
"- though I'd probably find more items I'm interested in given more time."
"I put the prerequisites I could find further down in the list, here, though I don't think computers made it on to the list. I was thinking of distributing the vaccines directly and then using the profits to reverse engineering the rest. Maybe leak some things to competitors so there's someone independent to work on it after I get accused of witchcraft."
"Door open to? My lab has a basement I can store quite a lot in - the vaccines in particular I don't think will take up much room so long as I make the needles and syringes and such myself."
"I think I can get people to take them if I pass it off as a new discovery and use my newspaper to advertise. Which I'm not normally comfortable using my newspaper for but it seems worth it in this case."
"Right, I'm just saying, it might be kind of hard to find a model of stuffprinter from my world that will do well at making hypodermic needles, people mostly use them for costume pieces and stuff like that where it's likely that nobody's already summoned a demon, gotten a batch of ten thousand made, and put them on the open market."
Lucien is torn between wanting to take this at face value (it makes perfect sense to him!) and finding it deeply suspicious that the interdimensional demon with a mind affecting aura would be so helpful.
"What sort of obligations to the Elves, if it's not rude of me to ask."
"The reason I can resurrect the Elves is because they have brain chips - not like mine, chips that store their whole personality and all their memories for them. And that also mattered to Melkor. He could take those chips, if he captured somebody. Copy them. Edit them. Make them have experiences without bodies to have them with. Any experiences he wanted. Faster than they would have been able to normally. He had trillions of them."
Lucien gets the sense that this demon could use a hug.
"Bringing them back shouldn't be difficult if there are Elves on board with it ... I'll need some spell ingredients and a place to do it in but probably you can just make those? Getting all of them on my Earth in very large quantities won't be feasible in the short term without a lot of hassle."
"Ingredients aren't magical. The entire process is scalable - right now it takes a few hours to sacrifice fifteen people to get back two but I can teach people how do it and run as many as needed in parallel. Might need more sacrifices to get back some gods I suppose."
"How long is a while?"
"I was planning on spending the next several decades researching the ritual until I got it to the point where it resurrected more people than it required to sacrifice. I guess I could still do some of that here though honestly I expect it would go a lot slower without access to my world."
"I think it would probably be easier to spend a century figuring out a better resurrection spell than to convince my world to scale-up massive necromantic rituals powered by trading sex to demons in order to resurrect the dead. The rest might be promising - celebrities don't scale but we can put on theatrical productions for demons who help."
"So one drawback of this taking place in your world is that demons don't already know about your world, so they're not already excited about your theatrical productions and celebrities, though I imagine with most your Alps would pass muster. We might wind up having to filter for history nerds who'll be really excited about the whole 1933 thing and I'm not sure what they'll want."
"Oh, you can totally sell it, it just - requires selling, instead of being something that every demon will already have on the tip of their tongue as soon as they notice they've been allowed to talk on summons. - people in my world get an afterlife, I don't know how that would interact."
"...maybe. I don't want to do either of my parents, though, they both got unusually good Limbo results - uh, dying to Limbo gets you one indestructible thing, like your favorite dog or a tree or a musical instrument or something, and she's got a camper van and he's got his entire house, and if this plan fails at some stage I don't want to have messed that up for them... My mom fostered some kids in Limbo, I can dig up what I know about those and see if any of them are good candidates. Pity we can't actually ask anyone..."
"That's convenient I guess."
Lucien ... is going to push the embarrassment into a box in his head. It is not helpful and he can deal with it later.
"I think than my only worry is the being a demon thing, even if you aren't native to my universe I am used to almost all magic things being at least as bad as there reputations and generally worse, even when this isn't obvious at first. I can probably address this by truth spelling you, I suppose?"
He actually has all the materials with him, - it's a useful spell. It will take a bit to assemble them since two of the ingredients need to be mixed shortly before casting and the small tree cutting needs to be refreshed with a technically separate spell involving a weirdly large amount of blinking but after a few minutes he can be holding the aforementioned branch and vial.
"Uh, you can refuse to answer questions if you don't want to - if you lie about minor things it might pick it up just as much as lying about major things. It also sometimes picks up misleading things as lies."
The original version of this ritual would involve eating the hair but Lucien managed to get adding his stomach acid to the vial to count instead so into the vial the hair goes. The liquid inside bubbles and turns silver and to a consistency somewhere between oil and mercury.
"So uh, have you, through action or your presence, affected my mind in ways other than the ones I am aware of and am accustomed to."
"...it sounded like you were not accustomed to being distracted by guys' abs. So far as I am aware I have never magically or supernaturally affected anyone's mind. I do know of some mind-affecting drugs I could in theory administer at range but have not done this to... I think anyone outside of medical school volunteer test subjects, but in particular not to you."
(The liquid bubbles but doesn't tilt to either side and the branch rustles but doesn't bend.)
Lucien has in fact been distracted by guys abs before like that but those were statues made by great artists so he assumed that they were meant to evoke that sort of feeling! Possibly he should reevaluate that assumption.
"Were you in fact a human, and if so did becoming a demon change how you think or feel in any supernatural or otherwise non-mundane ways?"
"I was. Being indestructible has some downstream psychological consequences but they're on the order of 'I spend a lot more time caffeinated' and 'I don't get sick so I don't spend any time in mental states influenced by being sick'; since being indestructible is magic I don't know if you mean for that to count as non-mundane or not."
"Makes it easier for certain sorts of entities to break through, can mess with topology, if you spend too long there you might go mad, that sort of thing? Uh, if you keep going some texts say it will eventually collapse into a raving dimension of mindless hate and chaos but I've never manage to find anyone who can operationalize what that looks like."
"Uh, I've seen obsessive fear, someone who wanted to eat everything, a guy who wanted to blow up the Earth for reasons I don't understand, someone who tried to have their family reenact the lives of the people who last lived in their house, and probably some other things I'm forgetting?"
"They might. I don't think they will be able to interfere from a world away, and we only need a hundred volunteers, and I haven't been getting the impression that they needed to wake up at any point in the process so there's no worry about getting their memories back to their mainline instances, right?"
"Uh, I might be bad at explaining this - I havn't really had the chance to talk about the details of the ritual with anyone I trusted with it before."
Lucien collects his thoughts.
"So the original resurrection spells requires each sacrifice contribute three times the amount of blood in a human body, typically meaning you had to bleed them several times and wait months for their blood to regenerate in-between bleedings. But there was a note in one of the versions of the rituals that indicated you could substitute in the blood of enough relatives of the sacrifice, with more blood the more distant the relative, and I eventually figured out that with a really really large amount of animal blood you could get it to work. But the fact that it's not their blood produces some byproducts - I'm not really sure what - that degrade the efficiency really badly after each use requiring even more blood. So I have a different spell that allows tentacles to sort of consume and excrete blood that turns out to work as a filter for removing the byproducts. Mostly filter - it still fails after enough uses."
"You need to put a lot of people in a sealed environment that can keep them all alive for years and manage a terraforming project at point B. Also, since you can't compel daeva to do things, you need to do this without being able to count on them for propulsion, fuel, or resupply. Also the people in the sealed environment need to not go crazy and kill each other. I think someone will pull it off eventually but there's not even people on every moon of Jupiter yet."
"Oh...."
"Basically everyone in my world would panic if they knew I was doing magic. And it's not like they're wrong to - cultists keep trying to destroy the world and dark magic kills far more people than mundane crime and I haven't actually heard of anyone who does as much magic as me and wasn't possessed by some sort of horrible madness or another. I've thought some about how to change this so I can sell people on resurrection once I get it but as it stands I have to keep everything I am doing extremely secret."