Carissa walks sedately and responsibly with her contract until she's nearly at Keltham's room, and then skips gleefully; she feels gleeful and she can't think of any reason to hide it with Keltham! Three Wishes!! Enough spellsilver for every project she can conceive of!!!! 

Knock knock.

Keltham is reading a book of cleric spells that has finally been returned to Ostenso's wizard academy, according to Ione, who has been diligently checking at least once per day.

This is some pretty strange stuff, frankly.

Answer answer.

"Hey! I have a contract with an option on my soul for you. Though, uh, the devil who wrote it for me said that I should not give you the option for free. Just as I wouldn't sell my soul for free, right - the consideration lends it dignity - this isn't an offer I make you expecting nothing in return but to see what becomes of me, it's a deal."

"Hell is so functional compared to Golarion.  May I have a look?  And are the rest of your arrangements settled pending this?"

"Here you go." Contract. "And no, the appointment where I settle the Hell side of it is in three hours. The devil I got would've been perfectly adequate if I were a fourth-circle caster at the Worldwound looking to make arrangements as a magic item enchanter when she died, but now I'm way more valuable and will actually need a higher-seniority devil who's authorized to make more expensive kinds of deals. Which in hindsight makes sense - being on Project Lawful made the other girls as valuable as a wizard a decade older and more experienced and powerful than them, so it makes me very valuable. Though the option decreases the value considerably, which I guess you can compensate me for."

"Oh, and how would I go about doing that?"

"Awkwardly, I feel like you've already asserted that if we're still together when we've built Civilization I will get mountains of spellsilver to play with. But maybe one of the mountains of spellsilver can be mine by right rather than a probable present."

"Not to be too unromantic but I can't actually promise you that until I know what spellsilver is fundamentally and if that quantity even exists in Golarion."

"But, if I just take that as indicating the general spirit of what's going on, then sure."

Keltham reads the contract.

The option itself costs 500gp for him to purchase, and wants him to pay 500,000gp if at some future point he'd like to own Carissa's soul.

This does not particularly square with the amount Keltham is expecting that Carissa is getting in exchange for her soul today, going on some past prices he's been quoted.

"Wait, I'm supposed to pay 500,000 gold pieces for you?  I bet the devil who's buying you today isn't paying anything remotely like that.  Are you conniving with this devil to make a profit off me here?  Who says you're even worth that?"

Keltham tries to say this sternly.  How's Carissa's Sense Motive doing against Keltham's Bluff?

Keltham is adorable and up to bluffing about as well as a Chelish ten year old. "No one in all the land would say I'm worth that. It is a truly ridiculous amount of money that even Abrogail couldn't pay."

"So if I can't make an insane amount of money or I'm not willing to pay this insane price for you, I don't get to be together with you into the Future, hm?"

"And here I was wondering if Cheliax just didn't understand romance at all."

"Well, you know, if nothing else I aspire to be a quick learner."

Part of him wants to optimize the part where, apparently, whatever devil signs this contract just gets all that money, but eh.  It's just 500,000gp at some point into the far future of their relationship.

"Well, think no less of me if I don't sign your very romantic contract upon the spot.  I do need to check the terms.  I don't suppose you asked the devil about unexpected unpleasantness?  Should've actually asked explicitly for you to do that."

"I did, I asked if any of the terms would have unexpected unpleasant effects, and he said, 'Tell the mortal that Glosialabolas, who made this compact, guaranteed this:  The deed that results from this contract's signing and its execution, will be as I expect that he will expect.  As for the consequences of the deed itself, time will show it.'"

"Are all devils so... Taldane doesn't have the Baseline word.  The thing that pronouncement has in common with saying 'Those above all mortals now battle.'"

"I haven't exactly met tons of devils but in stories, yes, they all are, even moreso more powerful ones."

"Well, they do them, I guess."

Keltham reads the contract, carefully; he has not actually heard a Lawful being pronounce it safe, only heard Carissa say that this was told to her.

...It would be legit pretty hard for this contract to hurt Keltham, though, there just aren't any sentences that talk about Keltham needing to do anything.

Except for the section that says the option can be voided if Carissa returns the 500gp to him before it can be exercised.  But even that section is just talking about something that happens to the contract, not something that happens to Keltham.

It would be an entirely unacceptable clause for a regular financial contract.  If the option goes up in price, the option purchase just gets reversed at the other party's will??  Part of Keltham's brain is repeatedly pointing at this and trying to yell about it what a bad deal it is.

The larger Keltham understands the message of the term perfectly well:  Sure, you can have her Future, if and only if she still wants you.

"Be it clear that I know perfectly well that it was the devil, rather than you, who suggested to you, or more accurately, told you, to include the term of this option where you can give me back the price I paid in order to nullify the option," Keltham says aloud.  "And then argued with you about it.  And finally told you that he wasn't executing the compact unless that term was in it exactly the way he put it down."

" - I didn't argue for very long! Devils don't give bad advice. But yes, I didn't want - I'm not trying to give myself an escape route."

"It's not an escape route for you.  It's an escape route for a different person named Carissa Sevar who might exist in fifty years.  Mortals probably look pretty changeable from a devil's perspective.  You can't expect them to know that all time-slices of you will be as one person in this, even if that's how the future plays out."

Keltham will ask for a lot of detailed explanations of a lot of detailed terms.

And then measure out 500gp of value, mostly in platinum in this case, from that small hoard he now has.

(It's actually a bit painful!  His legible asset balance just went down by a factor of 6!  It would be less painful if he had knowable repeatable ways of earning more!  But considering that he got this money by renting out Carissa, his brain rather needs to shut up about his legible asset balance.  The remaining 100gp is, in fact, exactly that amount he demanded and was paid for going through the etiquette lessons.)

He offers the money to Carissa.

Just in case he wants to spend forever together with her, at some future point.

She takes it. Takes a deep breath. Puts it in her Bag of Holding.

Signs the contract. 

Keltham signs.

(Having your alignment shift 12% of the way towards Lawful Evil doesn't feel like anything in particular.)

It actually feels kind of stupid, that this shifts Keltham's alignment. Not that she didn't already believe that the system was kind of stupid, but - they haven't made ...any progress, really.... on corrupting Keltham in the sense that matters, in the sense of making him someone who thinks like Asmodeus and will thrive in Hell. He still wants her to be happy, he's still pleased about the escape route, he's still-

Lawful Neutral. The kind of agent he wants to be negotiating with is in Axis. 

There is, Carissa realizes as she beams at him, possibly nothing she can do about that. It might be that she can only make him Pharasmin-Evil and not make him Asmodean-Evil and - it feels like a situation where accomplishing part of her objectives is worse than accomplishing none of them, a truly Asmodean Keltham would be an asset beyond imagining but one still Lawful Neutral in his heart -

- she cuts off that line of reasoning. She'll just have to persuade him of all Asmodeanism. 

...but Keltham's smile fades, before too long, as he remembers a thought, which is all too often a hazard to the people of dath ilan.

"Snuggles after you actually successfully make afterlife arrangements," Keltham says.  "I'm feeling too worried, deep down, until that part actually happens."

The possibility that Carissa has a hidden Zon-Kuthon cleric alternate personality is a bit of a moodkiller.  His life would be so much easier if all of these increasingly conjunctively chained thoughts were ones he could just categorize as Statistically Unlikely Awfulness and move on.

" - okay. Should I go, then? Leave you your books? Send you Meritxell?"