This was born from reading a bunch of fics where Leo has the one family member named Raphael who wants to re-connect with him (which could very well be a cannon thing, I haven't read the books since 2012/2013), and I might have run wild with the idea, as one does.

This is the style of story where you find out the background information as you go, which is very on brand for me. I know when this happens vis-à-vis the Riordan story-line, but when it comes to Shadowhunters, let's say this is absolutely outside cannon.

1. A chance encounter

Leo was running, which wasn't anything new really, but chasing after an amphisbaena as opposed to away from it was definitely new. Like, sure, he was a demigod, and meant to fight monsters, even if those monsters had two venomous heads, one at each end, chicken feet and feathers wings, like some sort of deadly amalgamation; granted that could be said of most Greek monsters, really.

The thing is, Leo is a demigod, which means that when he sees a group of very tattooed individuals having a goose chase with the mother of ants, he kind of has to intervene; even if he would rather not. So he pulls out the Warhammer he's been working on while on the road, and jumps into the fray, having to heat the metal to get through the creature's scales, but otherwise easily turning it into dust as per usual.

And then he's faced with four very shocked, very tattooed, individuals; who he only now recognizes are all armed with weapons he's never seen before. He takes the free moment to make sense of them, his nose can't quite decide if they're friend or foe, and they clearly were capable of seeing the monster; so Leo puts on his most charming smile.

"So, what's your pantheon?"

He watches them exchange glances, confused, which is fair really, he was confused about it too the first time he bumped into someone from a different set of deities. The girl with the whip and the killer looks is the one to respond, looking curious.

"We're Nephilim"

Leo's a little rust on his Latin, considering he's only been to Camp Jupiter twice, and will never be allowed in again if Reyna has anything to say about it; he's probably been vetoed from Camp Half-Blood too, though, so it's whatever. But eventually his brain supplies him with a vivid image he saw back in Italy, way back when; so maybe he's a little wary, sue him, Catholics have never been kind in his experience.

"Cool, angels are real too, that's gonna be fun to explain"

The blonde dude who makes Leo think of Mars, like, full Roman style Mars, takes a very threatening step forwards; or he tries to be threatening, Leo's seen Percy angry, so he doesn't think he can feel threatened by anything ever again.

"Who are you?"

Leo raises his hands, smile ever present, eager to see his expression when he says his introduction.

"Leo Valdez, son of Hephaestus, and I'm guessing your very first demigod"

He lifts the hammer from where he left it on the floor, laying it into his shoulder as he grins at the very varied expressions. The red head and the blond both look a weird combination of confused and surprised, whip girl is grinning just about as much as Leo, and the black haired guy has the look of 'this might as well happen'; Leo feels like he's learned something about them.

Whip girls fully approaches Leo, who stays firmly in place despite the mixed signals his instincts are shooting him, smiling brightly as she offers him a hand, her whip turning into a snake wristband.

"Isabelle Lightwood, welcome to Brooklyn"

Leo happily shakes her hand, watching her eyes do something interesting for a moment, he knows he runs hotter than normal humans, but he silently congratulates her in being subtle about her surprise. The red head approaches next, a little more cautious than her companion, but still very much curious.

"Clarissa Fray, but please call me Clary"

The blonde dude frowns.

"Clary!"

She turns to him, and her tone is one Leo's been at the end of way too many times.

"He just saved our lives Jace"

Then she turns back to him.

"What was that thing anyway?"

Leo makes a face.

"An άμφίσβαινα, they generally stick to Arizona"

It's a problem because it means he's not the only one with godly blood in this city, and that means there's probably a satyr nearby, or worse, someone Leo knows. The black-haired guy finally speaks, and it's then that Leo realizes he's got a bow in his back; he kind of looks like a male version of Thalia, maybe darker blue eyes.

"What does that mean?"

Leo figures he might as well, after all these people could very well help him figure out who the monster was looking for; if it's either him or someone he knows then all Leo has to do is lay low for a little and get moving once he's sure no-one's the wiser, but if it's a new demi, then things will get a little messier.

"It means there's someone with godly blood in your city, monsters are attracted to us, if you're lucky it was just looking for me"

The blond dude, Jace apparently, but Leo will keep calling him blond dude until the guy actually introduces himself; frowns a little harder.

"What if we're not lucky?"

Leo winces, not because of his tone, but because of a very potent flash of the past he would rather do without.

"City destruction, child death, the usual"

He unnerves himself with how detached he sounds, but it's the price of going rouge he supposes, because he got tired of being torn by the usual. Clary looks aghast, and Leo wonders what the Nephilim world is like that she can be.

"Child death?"

Leo makes a face, because he has a feeling that's exactly what's on the line; which means the risk of getting seen, which isn't something he's comfortable with, not when he's been so careful. And yet, he's still very much human.

"If it's a young demi, yeah, most of us don't get to live past 13"

Isabelle, frowns, clearly disturbed by this information, and Leo thinks Nephilim must really have it nice; he's met plenty young demis in his travels, only a sparse few times was he able to send them somewhere safe, and he's not even sure they actually made it, so he's become desensitized with death at this point.

"How do you know for sure?"

Leo bites the metaphorical bullet that's pointed at him, because this isn't laying low, and it could very well blow up in his face; but if he doesn't clear his doubts it'll become yet another thing he regrets forever.

"You wouldn't happen to know anyone with magic, would you?"

Isabelle throws a very pointed look at the black-haired guy with the bow, before she smiles at Leo; he has the feeling there's something there he's missing. But he figures it doesn't matter, it's not like he's gonna make a habit of crossing paths with the Nephilim once this is over with.