Aziraphale was pregnant, although he wasn't entirely sure how he knew. It wasn't like there were angel doctors with whom he could schedule a check-up to be certain, and human doctors were out of the question. But he had a, well, ineffable feeling that this was in fact the case. He was pregnant. And it was Crowley's.
It had to be Crowley's, of course. Aziraphale had never had sex with anyone else. Still, after six thousand years, not all of it friendly and nearly none of it as romantic partners, it gave Aziraphale a giddy sense of pleasure in knowing that it was the demon who'd managed to "knock him up" as he put it. Crowley had assisted him through every wave of his heat, which had come and gone at odd intervals, occasionally disappearing for weeks or even months at a time before returning, full force, to make him miserable. Well, miserable when Crowley wasn't knotting him, at any rate. It had gotten worse, as the Metatron had warned him, but they'd managed. And now he was pregnant.
On the bed beside him, Crowley stirred, squinting up at Aziraphale from under the cover of a large, black wing. "Alright, angel?" he asked. "Need another go?"
"Don't think so," Aziraphale said. The uncomfortable feeling of emptiness was gone, as if it had never been there in the first place.
Crowley's squint deepened, and he pushed himself half upright. "Are you...glowing?"
Aziraphale examined his hands. He liked to think he exhibited a low level of celestial radiance at all time, although deep down he knew this was probably not true. "I'm not sure," he said. "Do you think so?"
Crowley sat all the way up. He looked rather radiant, Aziraphale thought, with his wings and hair mussed and his gorgeous yellow eyes exposed. Aziraphale often wished Crowley wouldn’t wear the sunglasses that hid his eyes from view, but after several hundred years of watching humans react rather badly, he certainly didn’t begrudge the demon for practicing safety. "Definitely glowing," Crowley said, aforementioned eyes narrowing further, and then widening. "Are you..."
"I rather think so."
"Christ," said Crowley.
"Oh, I hope not," said Aziraphale. "It'd better not be His, for one thing." Angels didn't consider Him their father the way humans often assumed, but it was an unappealing thought nonetheless. "Is it noticeable, do you think?"
Crowley eyed Aziraphale's stomach doubtfully. "It shouldn't be. We only just did it last night."
"I meant the glowing."
"Oh." Crowley looked up at Aziraphale's face. "Nah," he said, and smiled. "Not to most humans, at any rate. And there aren't many nonhumans, occult or ethereal, kicking around the planet these days."
The thought of Heaven dampened Aziraphale's good spirits. "They won’t be happy about this, will they?"
"I doubt it. An angel and a demon having a kid? It's unheard of," Crowley said. "Would be even if that was something you could do before now. Our...sides aren’t exactly known for mingling." He said the word ‘sides’ with the uneasy sound of someone remembering that technically, they didn’t belong to any sides except their own anymore, but wasn’t sure how else to phrase it. Aziraphale forgave him for the implication.
"I don’t think it's technically mixed, is it?" he asked, stroking his stomach. "I mean, you were an angel before you were a demon, after all."
Crowley contemplated that for a moment. "Maybe," he said, "but I don’t expect Heaven and Hell will see it that way. And anyway, I'm a demon now, aren't I? That’s bound to count for something."
Aziraphale hummed thoughtfully.
"Half angel and half demon," Crowley said. "I don't even think there's a word for that. Do you?"
"Oh, probably," Aziraphale said, although despite being very well read he couldn’t actually recall. "Humans like coming up with that sort of thing. Anyway, I stand by my initial assessment. If it's a matter of genes, the child will be more angel than demon anyway."
It was, in all probability, not a matter of genes. Metaphysical pregnancies, rare though they were, generally weren't about genetics at all. But the universe could be pesky at times, and liked to play tricks, and so Aziraphale could very well have been right.
"It’s like with Adam," Crowley said. "It’s not about the genes. It’s about how we bring it up. Good and bad influence." And he was definitely right.
"That's good, then. If you're correct," said Aziraphale.
Crowley blinked and gave Aziraphale a questioning frown. Aziraphale explained, "The child will have one not-quite-angelic angel parent, and one not-so-demonic demon parent. Everyone else close to the family will be human. That's about as neutral as it’s possible to get."
"And you want it to be neutral?" This was news to Crowley, who had rather expected Aziraphale to be taken with the idea of raising the child for Good.
Aziraphale fixed him with a firm look, eyes narrowed. "I want it to be a good person. But that doesn't mean I want it to be Good. And I most certainly don't want it to be Evil." Which was fair enough.
They were both quiet for several minutes, absorbing the information.
"We're going to be parents," Crowley said.
"We are," Aziraphale echoed.
Another few minutes.
"How much do you know about babies?" asked Aziraphale.
Crowley shrugged. "Not much." Nothing helpful, anyway. Most of what Crowley had learned about babies over the years had to do with how much they irritated everyone around them when they started crying in public. Even Warlock's second-hand rearing had taught him very little. "I was hoping you'd have a book recommendation or two."
"I haven't read any books about babies," Aziraphale admitted. The only books he'd read about babies were the sort of book that involved a mother dying in birthing a child who would grow up for some great and terrible destiny. He hoped this pregnancy was not that sort.
“Probably ought to before it comes. Nine months, do you think?”
“Could be. Could be more.” Angels lived effectively forever, after all, unless something happened to get them killed permanently, and that was incredibly rare. Aziraphale had gone on reading binges that lasted longer than nine months. He knew Crowley had taken much longer naps.
“We’ll need to pick out a name,” he said. “Not Biblical, I suppose? I imagine you’d be rather against that.”
Crowley shrugged. “It’s not like most of the people in the Bible had anything to do with me. Long as we don’t name it Michael or Gabriel…you know, the big angels…”
“Fair enough. What about something Greek, maybe?” Aziraphale mused. “Classic Greek names are wonderful; Nymphodora or Cassandra…or something from astrology, like Bellatrix or-“
“Not Bellatrix,” Crowley complained at once. “Astrology name or not, now that Rowling’s books are part of mainstream culture you can’t go naming a kid after one of the villains. And Nymphodora’s out too.”
“I thought Nymphodora was one of the heroes?” Aziraphale asked. He’d read Harry Potter, and determined it was a lovely read, if one ignored the glaring plot holes and an author who refused to shut up.
“She is,” Crowley said. “But I hate the name, and mark my words, the kid will too. Besides, it’s too early to pick a name. We’ve only just found out. And those are all girls’ names. We don’t even know that it’s a girl yet.”
“I don’t think it will be a girl,” Aziraphale said. “Or a boy. It’s not as if angels or demons experience gender the way humans do, so I don’t see why a child of an angel and a demon should be any different. And anyway, there’s no such thing as a ‘girl’s name.’ Not really. The way I see it, it makes just as much sense to give it a name now, and let it change it later if it likes, when it’s old enough to think on it properly.”
“Might be best to stop referring to the thing as an ‘it,’ then,” Crowley said. “Ought to start calling it ‘them,’ I reckon.”
“I suppose you’re right.” Aziraphale rested his hand on his stomach and looked down at it. “You know, I really didn’t expect this.”
“That piece of your biology was turned off. I hoped, of course, but I wasn’t sure you’d actually be able to do it.”
“You don’t regret it, do you?” Crowley sounded worried, and when Aziraphale looked up at him, he looked worried too. His brow was creased, and his long tongue kept flicking out to wet his lips.
Aziraphale took both of Crowley’s hands in his. “I could never regret this,” he said. “I asked you. I wanted us to be able to. I just thought I might be disappointed.”
“In other words,” Crowley said, bringing their joined hands to his lips and kissing the backs of Aziraphale’s fingers, “you doubted.”
Crowley smiled. “I always find it funny. When you doubt and I have faith.”
“I don’t find it funny at all.” Aziraphale allowed himself to be pulled in, and Crowley rubbed his nose against Aziraphale’s and then pressed a brief kiss to his lips.
“We’re going to be parents,” Crowley said, grinning.
In spite of himself, Aziraphale grinned too.
 That was probably the biggest clue for Aziraphale. Even between waves of heat, there had still been a sense of emptiness inside him, subtle but irritating, and of course gradually worsening until Crowley satisfied it with a knot.
 The thirteenth century sprung immediately to mind.