WHOOP WHOOP okay just to preface this, most of this is me going “hey i think being a kid of poseidon is a weirdly complex experience”
i think this is canon officially but percy’s music taste is one of the 78378837 things in his life he got from his mother; sally’s an old-school rock and old-school rap diehard, and percy follows right in her footsteps, because on days when gabe wasn’t home sally would turn their shitty little radio that sat on the kitchen countertop on and bang her head while cleaning or cooking or shuffling bills. trips to montauk were sally shouting the lyrics to an AC/DC song and tiny percy not knowing the words but wanting to join in, so he’s just shouting nonsense. a lot of the things percy likes, he likes them for sentimental reasons, and music’s just another one of those things.
when percy was first born for three weeks he would literally not stop screaming. he would not shut up. he would sleep for half an hour and then he’d scream for three. and then sally gives him his first real bath, and percy is the happiest he’s ever been since he’s been alive. i have in my head a very comical image of sally pulling percy out of the little tub and he starts screaming like a banshee, and then she sets him back down and he’s back to giggling happily, rinse, repeat - so eventually sally learns that she can clean the kitchen sink really good, stop it, and just drop percy in. after she figures that out he’s an insanely easy baby, and also toddler, because imagine if you could just dump a cup of water on your kid’s head and he’d just instantly be less upset. the downside to this is that water gives percy a lot of energy, but sally would rather be chasing a giggling toddler than a screaming one.
because of that, growing up, whenever percy was angry or upset and sally couldn’t immediately calm him down because she had to wrangle gabe, she’d tell percy to take a shower. percy takes showers based on his current mood. he thinks everyone does this, and one time at his first summer at CHB, annabeth is upset about a fight she had with someone in the athena cabin and percy’s helpful advice is, “maybe you should take a shower?” and annabeth gets so pissed because she’s 12 and she thinks percy’s telling her she smells. percy is extremely confused.
if he’s ever landlocked far away from the coast for a long time, he gets antsy and irritable and depressed, which is not something they figure out until annabeth’s first job involves her relocating to denver for six months and percy goes with her, and it is a truly hellish six months. they figure it out when they stop off at CHB on the way home because maybe percy just needs something familiar, maybe he’s just homesick, and then he proceeds to stay under the ocean for three days straight
while i’m thinking about headcanons relating to percy being half sea god, this kid drinks a truly astronomical amount of water. he’s like the king of the hydration nation. he has a reusable water bottle of truly monstrous size that he has to fill up every hour, because he is the most hydrated person alive, and he has been known to sometimes just stick his head under the faucet and drink directly from the sink like an oversized dog. beverages that are not water are unacceptable. annabeth, who lives off of tea, coffee, and red bull, thinks this is weird.
half sea god metabolisms go hard because percy’s body, although he doesn’t realize it because he’s never lived in the ocean, works doubletime when he’s not in the water. he eats so much because it takes more energy for him to exist on land than it does for literally anyone else. zeus and hades kids have it easy, they’re literally always breathing air or walking on land, they’re in their natural element just all the time. percy’s magic godblood is just screaming “what the fuck is this what the fuck is this what the fuck is this” and that’s why percy eats almost an entire meal every three hours.
further Percy’s Blood Is Half Seawater headcanons include: he has never owned an umbrella in his life because he just trots through the rain like nothing in the world is wrong, he’s not only more resistant to heat but also resistant to cold because the ocean’s pretty damn cold most of the time, he has a high tolerance to mortal drugs so when he gets sick not even the tamiflu can’t save him, if he’s near the ocean he gets really bouncy at incoming tide when the waves are strongest, always knows whether it’s an el nino or la nina year, and he doesn’t know it because NYC isn’t exactly at risk for hurricanes, but the closer he gets to natural ones the more batshit he goes. completely chaotic, can’t focus on anything, running around like a chicken with his head cut off.
living on a fault line or near a fault line is a NO GO he CANNOT DO IT. not just because percy accidentally triggering an earthquake on a fault line could Fuck Shit Up, but because the constant tension of the colliding of the tectonic plates puts him on edge. he gets stress migraines near transcurrent faults. being near intense volcanic activity for a prolonged amount of time, like living near an active volcano, just makes him angry. sometimes he gets inexplicably frustrated when traveling, it’s just because they’re over a failed ancient rift in the middle of a tectonic plate. and percy accidentally triggers a lot of earthquakes, but since they’re all intraplate quakes and he has no idea he’s doing it, they turn out to be more like lil tiny tremors, and people just kind of... don’t notice it. no one figures this out until after the giant war and percy’s struggling with night terrors and those tremors start getting a lot more noticeable. percy, annabeth, and grover have to go on a Recovery Roadtrip because staying in one place means percy’s doing a lot of damage to one specific area of a gigantic tectonic plate and creating a weakness in the earth’s crust increases the tectonic stress making subsequent earthquakes worse and also i fucking think they deserve a roadtrip what the fuck!
being a kid of poseidon needs to come with a goddamn handbook, but it’d be 1000 pages of the wildest shit imaginable, like “if you need a blood transfusion there’s not going to be any human that can help. you’re going to have to find a willing horse or ocean creature, and pegasi do not count” or “if you ever have the urge to just knock back a salt shaker like it’s a shot of vodka, that’s also normal, and encouraged”
i’m pretty sure canon contradicts this but lol canon is mine to ignore, but i think because of gabe’s tendency to be a gross human being, percy has grown into being a neat freak. annabeth leaves one (1) empty can on the table and percy makes distressed percy noises about how they HAVE A RECYCLING BIN, BABE, TRASH DOESN’T BELONG ON THE TABLE - also because of gabe, percy gets weird around alcohol and the smell of beer makes his heart hammer. which is awkward, because sometimes the older CHB kids who survived the titan war and the giant war celebrate being alive by sneaking in alcohol, and chiron will turn a blind eye to it because CHB is one of two places in the world where demigods are safe to be off their game. mr. d is seething, but, you know, that’s fine. so percy spends those parties cleaning up after people and cutting people off when they’ve had too much and chatting with the people who got drunk but accidentally got sad drunk. if they’re on the beach and the waves are crashing harder than usual, well, they’re a bunch of demigods excited about being alive, and no one really notices.
extremely good taste in sneakers he just wears those sneakers with like, the worst outfit imaginable
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