Disclaimer: I don't own Percy Jackson, its concepts, or its characters. No money is being made out of this.
The weirdest part is not knowing.
At least, at first. And Nico makes sure he continues to focus on that, because the alternative? Is to be terrified she is his, and Nico makes it a habit to avoid feeling terrified whenever possible. He gets enough of that just from being a demigod.
He's pretty sure he's mostly failing, though, if the constant undercurrent of dread in his stomach is anything to go by. And it may be the weirdest part, but not by far – pretty much their entire situation is weird as hell by human AND demigod standards.
Annabeth and Percy try to forget all the weirdness; they try to make everything seem normal because that is how they cope. They think they're helping Nico, too, and he doesn't have the heart to tell them it's the opposite: he tries to stress the weirdness of their situation in his head so he doesn't have to face the mundaneness of it: that he has a real family now, people who care about and depend on him, and that he is about to become a father.
Because either way, they're all going to parent it. Her. Him. (Annabeth insists that it's a girl, but they don't actually know yet; they did an ultrasound but it didn't show anything conclusive.) But he can't help it: it feels worse if the baby is biologically his. He tries to reason with himself: the responsibility is thirty-three percent his regardless, after all, but the pressure is just there. He isn't ready for it to be his. Percy and Annabeth were already a thing before he came along – how wrong would it be for their first child to be Nico's?
(It suits him just fine to be the third wheel in this tricycle. It feels…safe. Comfortable.)
"That's just because you haven't met her yet."
He suppresses an eye-roll as he runs his hand over the smooth, rounded wood railing of a crib. "I highly doubt that."
"It says so in, like, three of the books I read," Annabeth continues, slightly out of breath. A crease appears on Nico's brow as he wonders if that's normal; if she's just nervous or if it's because of the pregnancy; if there's enough oxygen getting to the baby, if the baby's stealing her oxygen. He looks around again, knowing he won't find Percy; it's just the two of them this afternoon. It makes him more anxious. "It's hard to make a connection with someone you can't see or feel."
"It's not hard for Percy."
She threads her fingers through his – it's so casual, so normal – and pulls him toward another section of the store. "Of course it is, honey. I'm surprised you're buying it – he is more terrified than you or me."
"Again, I highly doubt that." Her fingers tighten around his and to his eternal surprise (because it's possible he will never get used to loving Annabeth too), he is comforted by it.
Nico is distinctly aware of the picture they make, just the two of them here without their buffer – she in yoga pants and a long shirt, her swollen belly making their purpose in the store self-evident, and he in ripped jeans and a beat-up leather jacket. Not the most promising picture of parenting effectiveness, and for all these people know, he's it – he's all this baby has for a secondary caretaker (father, he corrects himself). But for the moment, nobody is staring and judging, and he lets himself embrace the fact that what he shares with this woman, probably no one in this store is remotely able to understand. They share the love of their lives. And now, somewhat awkwardly at first, each other – and soon, more.
He lets go of her hand and steps behind her, experimentally (always experimentally), as a store employee approaches them; Annabeth dismisses her assistance ("I'll let you know when I need anything, thank you;" as if she'd need any help with interior design of all things) as Nico places both hands on her stomach and his chin on her shoulder. It's slightly awkward; he's the tallest of the three of them. He half expects her to move away; they don't do much touching alone, and especially not in public. But she leans into him and covers his hands with hers.
"What do you think of that one?" she asks, pointing to one of the color samples in the big book she was looking through. It is a pale yellow; 'Paper Moon', it's called.
"I love you," he says, and places a kiss on her shoulder.
She turns her head to face him; the surprise in her expression makes him self-conscious. "I love you too," she says simply, giving him a small smile and nuzzling his cheek. "But focus. How about this one? I know we'd discussed blue, but everything else is already blue in her room; I thought we could branch out a little."
He looks at it again, but his eyes are unfocused. The only thing he can think about is his (Percy's?) child moving underneath his fingers. "It's fine. It goes well with blue."
"I agree," she says, and he can feel her smile next to his cheek.