au where aaron and neil meet as kids. they bond. they're friends. they're the only friend the other has. and then neil is ripped away and they never see each other again until they do, and they recognize each other but say nothing. aaron bitches at neil for the first few months because he's pissed. neil bitches back because it wasn't his fault and also aaron's a piece of shit now (not that he wasn't before, he was just more innocent then). aaron, when he picks up on andreil, drags neil away and does a few things:
a) he rants in disbelief that neil would go for andrew, of all people,
b) gives him a shovel talk, and
c) finally, for the first time since they reunited, hugs him.
things smooth out after that, and the team picks up on it. allison asks, and andrew looks at them the way that demands an explanation, but neil and aaron silently agree to just...not say anything.
they're entitled to a few secrets (neil has to bite down the bitter laugh when aaron says this) and it's sort of fun to fuck with people, anyway, so they just keep on doing what they're doing.
it comes out a few days after seth dies, when aaron and neil get into a fight. it's bad, nearly turning physical (the team all being there and witnessing it is the only thing that stops it from turning physical), and they start referencing things from their childhood.
"says the guy who cried after Joey Lopez called you a loser," neil spits.
aaron bristles, his fists clenching so hard his knuckles whiten. "at least i never threw up on stage!"
and on and on it goes until wymack shows up and breaks them up. they refuse to explain, after, even to andrew and nicky, instead just avoiding each other. but then christmas rolls around, and neil is still adjusting back to normalcy (as normal as it gets there, anyway) and he's full on dissociating at one point, and no one can bring him out of it, until aaron sits next to him, within reach but not touching, and starts talking about some bullshit gossip katelyn had told him.
neil comes back to himself slowly and slumps down onto aaron's shoulder, who, to the rest of the monsters' surprise, barely reacts. finally, they explain (but only to the monsters) that they knew each other for a few months when they were young. neil mentions offhand that he used to have these episodes (because of his mom, which goes unsaid, but aaron's face darkens and he wishes he had andrew's knives so he could go beat her up) and that aaron figured out how to help. aaron had become a safe space for neil when they were younger, and neil for aaron, and neil's mom tore them apart when she forced neil to pack and leave without letting him give aaron any warning, leaving aaron to assume he'd been abandoned.
now that others know, aaron lets himself slip up and call neil danny, because he'd gone by daniel sims when they were kids (at neil's permission, obviously, and it actually does help center himself after the nest - a reminder that he is not nathaniel. he has not been nathaniel for eight years, and he will never be nathaniel again).
and...that's all i've got.