"Discouraging. Ah, well, I take it that if it takes a few centuries to get the skill level to reverse this you'll both be around, which gives you a profound advantage over most of your kind."

"Our parents might not be, though," she says, subdued.

"I have no children, but if mine vanished and I could prevent my aging while working magic that would eventually make me powerful enough to find them, I cannot imagine I wouldn't immediately do that."

"Our parents really shouldn't be doing more magic. Both of them had really terrible people for teachers who encouraged them to pursue specialties for which they had great talent and little mental resistance. If they did enough magic to get strong enough to find us then we'd probably have lost them anyway because they wouldn't be themselves anymore."

"Oh. I'm sorry. Can't they respecialize?"

"Theoretically, yes, but--there's a lot of context here. So, the first thing you should probably know in my mother's case is that the man who taught her magic first murdered her parents and kidnapped her, and in my father's case that his teacher was his mother, but the only reason she had him was because her husband wanted a child, and my grandfather died shortly after Father was born. There's a reasonable doubt as to whether either of them are capable of having a healthy attitude towards practicing magic." She shrugs. "Besides, we vanished from a murder attempt. It's not necessarily reasonable for them to assume we're alive."

"I see. I am very sorry." He stands. "Shall we go outside, and work there? It's a beautiful day and I cannot shake the feeling that my human allies are going to be distressed with me over this even if it's no problem in your home nation."

"I've never actually had to deal with people who had their minds so far in the gutter that 'teaching magic' wasn't a perfectly plausible alternative to 'having illicit extramarital sex,' so I can't help you there. But sure, we can work outside."

"What?"

"I mean, Genosha doesn't get a lot of casual visitors, it's hard to get to without a mage, and everyone there has a huge respect for magic. Even people who'll tut about people being unsupervised together relent if it's for magic."

"The general basis for the mortal custom that men and women shouldn't spend extended time alone together is fear that they will be having sex?"

"...Yes? Premarital sex is almost always a big deal in cultures without decent birth control."

"You're using several concepts that aren't translating."

"...So if a woman has sex without getting married first she could end up having a child out of wedlock and this is usually considered a bad thing? I'm not sure what isn't coming across."

"That one can have sex without getting married. We can't do that. I take it Men can, and now that you mention it that makes some other things make sense, but no one ever said so and it's rather absurd. Also your'e saying 'end up with a child' like that could happen to unmarried people, or accidentally."

"Human babies happen when you have sex with someone of the opposite gender without taking appropriate precautions. Why, how do they happen for your species?"

"Two married people decide to produce one and focus very very hard on that goal. We don't do it in wartime. We don't do it if either parent will have pressing obligations in the next fifty years, or have to be absent at all in the next five."

"That sounds far more sensible than our way, but since my sister and I were an accident I think I'm grateful that humans work the way we do."

"I see. 

Among my people it would be a very grave insult to suggest that I'd have sex with children who I spend the evening working on magic with privately. That's probably why none of the men explained their custom."

"...I'm not a child. I know I'm incredibly young compared to you, and have an appropriate lack of experience, but my brain has finished developing and I'm reproductively mature. And, um, yes, there are generally exceptions to the rule when children are involved."

"Nonetheless." 

He sighs. "Do you know how many people I'm going to have to explain that to? Everyone's been utterly confounded by Men, we have trainings on how to collaborate with them without inadvertent serious cultural misunderstandings, this rule features in them, and it's because they can accidentally have children!"

"I would have told you sooner if I knew you didn't know!"

"I'm not upset with you! There've been more absurd cultural misunderstandings, some of them thought all of us were adolescents once because we don't have facial hair, some of them thought we live forever by drinking their blood, and in hindsight - actually, in hindsight, a number of things are explained as actually being about Mannish sexual mores, I should really have pieced it together sooner. 

In which case I wouldn't have given you my bedroom. Sorry about that."

The rock on the table has crumbled into dust.

"That's going to make it so much worse if anyone finds out. I won't tell if you won't."

"And two hundred other people don't," he grumbles at the pile of dust. "I'm not marrying you."