Keltham is briefly shocked that Carissa is escalating that fast, then rapidly questions his first impression and realizes that symmetrical-mouth_application may be a specially convenient case for interplanar romance because he can just mirror whatever she does using the same appendage.  A few moments later, he is surprised again when all Carissa does with her mouth is apply a brief light suction to his own lips.  Deliberate teasing?  Anyways, Keltham will just apply some brief light suction right back.

Carissa would normally be more stressed out by trying to interpret all Keltham's facial expressions - is he confused?? - but this is in many ways the least stressful situation she's been in in a day and it's one she's possessed with instincts for, unlike trying to serve Asmodeus which humans are known to be terrible at, so it's easier to just go with it and set all the interpretation that's not immediately necessary aside for later. She pulls away slightly but leaves her hand on his shoulder. "By normal Chelish standards if you haven't negotiated anything eccentric," she says, "we have now departed the range of things you're supposed to do if you have a monogamy-agreement with someone else, but not the range of things that let you say 'what? we're not even slightly sleeping together', and we haven't even entered the range of things you can make other girls jealous with in the morning."

"By dath ilani standards, we're probably somewhere at around 5.1 out of 12 on the Standard Romance Escalation Lattice-Scale, on the pathway where we have sex to become friends instead of the other way around; though the thing you did wasn't standard enough to have a standard rating and could maybe have been 4.8 instead, which would be a good deliberate-ambiguity-maneuver if this were Complicated Romance.  You'd be allowed to do it with anyone else you wanted under all but the strictest quarter of monogamy agreements.  It wouldn't enable you to take my clothes and their informational-private-property as a trophy in a socially acknowledged way that let you get away with wearing my stuff to class tomorrow, because that is far too perverted a practice for a young person like myself to have heard about it."

"Oh dear! How perverted will I have to spend tonight making you for that to be a practice that you expect a similarly perverted person back home will have encountered."

"Your goals are unrealistic but you shouldn't let that stop you from trying."  Keltham leans forward, slowly in case she wants to object, takes Carissa's head in his hand, turns it gently aside, and very lightly nibbles on her ear, just about exactly as long as she kissed him for.  "Five point two."

 Why is he being slow, is that considered more romantic in dath ilan or something? Normal people don't have sex to become friends, they have sex to have sex, or to be useful to someone else who has something they want, or to put someone in a compromising position of some kind. She is going to mention none of these confusions. 

"There's no such thing as unrealistic goals in Golarion. ....unrealistic timescales, maybe. But I'm optimistic. See, my understanding is that we'd fall right off those dath ilani scales if you bite down, now. And once you're off the scale, well, anything can happen."

(without any conscious thought at all, in a fragmentary perceptual moment, Keltham arrives at the meta-level conclusion that he has been prompted to fast action and therefore fast thought)

- okay but how hard exactly is it okay to bite down she probably does not mean he is supposed to literally actually bite off a piece of ear or maybe she does -
- there are healing spells here, he needs to worry less -
- Keltham himself has the power to heal, granted him by his deity still unknown -

Keltham quickly clenches his left fist, presses his fingernails into his own palm in order to get a very quick concept of how much force might correspond to how much pain, quickly increases the pressure until the pain seems substantial, more than merely noticeable, and then bites down around that hard on Carissa's ear.

She gasps, not unhappily. "There, see, where are we on your scale now, dath ilani?"

Along the Standard Romance Lattice, on the most common pathway where first you have sex and then become friends, the steps would be numbered as follows:

0 - Assumed prior knowledge: commonly known mutual possession of the human heritage, and of default frameworks laid down by Civilization.
1 - Mutual determination of probable receptivity to flirting, via passive or non-flirtatious information-gathering.
2 - Active flirting while maintaining plausible deniability.
3.0 - Overt common knowledge of mutual attraction achieved.
3 - Teasing or being nice to each other without physical contact; maneuvering for later relationship advantage.
4 - Physical contact.
5 - Overtly sexual contact.
6 - Sex with genital participation.
7 - Maneuvering around whether or not to go on a second date.
8.0 - Common knowledge established of a relationship extending beyond a single encounter.
8 - Dating, learning more about each other.
9 - Taking on obligations and commitments inside the relationship; revealing of nontrivial private info to each other with attached secrecy obligations; less-than-maximal-ogamy arrangements for those into such things.
10 - Having a child; or childless marriage lasting at least 15 years.
11 - Long-term to indefinite marriage; multiple children if so desired.
12 - Intention to be together in the Future for eternity.

Technically according to this scale, Keltham and Carissa have yet to achieve Step 0!  Actually, that's not just a technicality!  That part is, in fact, quite important!  But the most correct answer to the intent of Carissa's question... would be that the Standard Romance Lattice doesn't consider the current depth of perversion* as a detail that matters to assessing the rest of the scale.  If adapted to include sadomasochism in the obvious way, it'd parse up stimulation by pain into an equivalence class of other acts that produced around the same amount of arousal in the target.  If Keltham knew how much of a sexual act biting Carissa Sevar's ear actually is to her, which he doesn't, he'd probably put that at around 5.7 on the standard scale.

(*)  Lit. 'sexual overcomplication'.

"We have gone forever outside of what is conceivable to Civilization.  Now that I've bitten somebody's ear, no city would allow me to enter there, even if I could return to my home plane again; none of them would consider me a dath ilani anymore."

"- not literally, that's humor with a straight-face.  I will also not include this disclaimer in the future unless you tell me to do that."  He bites her ear again, slightly harder.

Gasp. "I can tell by - reading your expressions. And also by - knowing enough now to guess that your returning home would be a national emergency in a fashion that had nothing to do with sex. There would be SO MANY important people asking serious questions before we could arrange - imports of girls who like being bitten. - you won't harm me by accident. 's actually hard, for people who haven't practiced it, to bite another person like they'd bite a steak, and I'm third circle, that wouldn't harm me."

"Wait.  You being a third-circle wizard means that - even if I tried to bite your ear literally as hard as I can, you wouldn't need a healing spell afterwards?"  Keltham will have Additional Questions about this later, but right now, the notion of biting her ear without being careful or worrying about it is tapping something deeper.

She kisses him again, a little more forcefully. "Yes. That's right. There are six competing theories of why and I will tell you none of them unless you tickle them out of me."

Keltham kisses back, running his tongue lightly over her lips, and then draws her own lip into his mouth and bites down HARD without holding himself back.  (If it was just ears but not lips, he's got healing.)

In some alternate universe where higher-circle casters only have less-vulnerable ears and otherwise normal vulnerability Carissa would be bleeding - well, long ago dead at the Worldwound, actually. Instead she leans into Keltham and shivers. "Quick learner. 's a good trait. You're pretty lucky, to have both 'a girl you can hurt' and 'a girl you can't really hurt' for the first time at the same time."

Keltham is now very hard, and he didn't even notice that happening to himself at the time because he was distracted.  "No - kidding.  I don't know how it is for men here, but - I get the distinct impression that being able to do what I want to you without holding myself back, and have you react sexually to that, is much - more the thing I'm discovering, than applying small careful amounts of pain - I think I'm ready for this to move to a cuddleroom."

"Or repurposed bedroom.  Could be my bedroom, even, if you're pretty sure your magic lets you do to the bedroom afterwards what you did to my clothes."

"Magic can clean it. But also I recall a bedroom at the bottom of these stairs." She holds herself back from examining the zippers too closely, even though suddenly they're right there to look at and they're fascinating, incredibly uniform down the whole seam and - wrong for the mood, right now. 

"You're the native!  The alien will trust you about whether we can do that without prior authorization."  Keltham stands, offers her a hand.

(Keltham has noticed where her eyes were drifting, of course.  The prior probability for that wasn't low.  He would definitely be checking out the hot alien chick's technology, in an appropriately analogized gender-reversed position.  He's not much worried about IP theft, though; the real trick to the zipper isn't going to be the interlocking shapes, it's going to be cheaply making a thousand copies of those interlocking shapes.)

She takes his hand. "If we break the bed I'll simply tell the facilities staff that we were studying dath ilani sex tradition, and productive interactions with the Golarion sex tradition of having a girl you can do as you please with."

There's whole strange worlds opening up to Keltham, though he's not at all sure he's understanding them correctly.  The notion of having a woman you can do as you please with - well, there's the version where you pay a sex worker so that you don't have to worry about their pleasure except insofar as it pleases you to do so, a sexual asymmetry balanced by a financial asymmetry going the other way - or by knowledge going the other way, in the variant Ione offered him - but the notion of a woman who doesn't allow you but wants you to do as you please, wants you to hurt her - 

He'll sort out later what's going inside his mind.  He may be ordinarily accustomed to knowing more about what goes on in there, but he doesn't have to sort it out right now before having sex.

Keltham grips her hand harder, because he felt an impulse like that, and pulls her after himself toward the stairs going down, because that feels like the right thing to do.

Possibly she is going to take this too far and push Keltham to uncover desires that she actually has to use a lot of will and acting ability and preparation-for-the-cleansing-fires-of-Hell to keep up with, and she should instead be trying to push him in smaller steps, but then she would lose the contest, and she's very competitive. Also if she pushes him very far then the other girls who are mostly younger will have a harder time keeping up. Yeah, this is a good plan. 

She follows.

Keltham is entertaining Suspicions about how many planes of existence, exactly, just happen to contain women who like totally want you to bite their ears and lips, and will derive their own sexual pleasure from it, instead of disliking pain in accordance with all sane evolutionary logic, and also they won't end up actually injured if you do that, and how likely it is that he would end up someplace like that just at random, but he will think about that later.  If some unknown force throws you into a suspiciously sexually compatible universe, the optimal response should include fucking that universe and not just contemplating how suspiciously sexually compatible it is.

Once they're down the stairs, he'll give Carissa a sudden surprise push to the bed, and then be about to leap on her when he remembers the existence of windows and doors that need closing.  "Wait here," he says, the words coming out a little more forcefully than they should have, and goes to try to seal the room insofar as that seems to be a thing.

The room has a door to the hallway, a door to the private bathing rooms, and a door to the balcony; it has one window, opposite the bed and positioned to shed light on the writing desk near the fireplace, with heavy curtains presently drawn over it. The door to the hallway and the door to the balcony both lock to keep people out. 

"Looking for something? Fireplace pokers are the kind of thing I'd need healing spells about."