AN: Got this idea because we know the gods have multiple aspects. The books only tap into 'Greek' and 'Roman' but there's actually a third. Mycenaean, the OLDEST form of them. For example, Mycenaean Poseidon was actually the king of the gods and the lord of both sea and underworld (Hades is considered a split of that Poseidon). We also know that Momma Jackson is awesome so in this story she was able to bring all the disparate aspects of Poseidon together into a unified being for a time which means Percy is a child of Poseidon, Neptune, and Mycenaean Poseidon. It fits with how busted he is in the books and the fact that he speaks Latin AND Greek early on.
Son of Three (First Look)
-Chiron-
Standing by Thalia's tree, having been compelled to watch the boundary by some unknown force, Chiron gazed out down the road. Despite the rain falling heavily outside of the boundary, the camp itself was dry, the campers eager for the game of Capture the Flag that would be starting after dinner.
Smelling something even though the storm, he turned to see a figure walking down the road. He could see three more figures further back, watching, before they vanished in a flash of divine light, but he could tell at least one was a mortal.
The gods couldn't interact with their children directly but perhaps a divine ally or two escorting a child and the mortal parent to camp? Such a loophole was well within the rules. As the child got closer he got a good look at them and was stunned by the intensity of their resemblance to the Sea god.
As a general rule of thumb, there were three metrics that determined a demigod's power.
The ones that couldn't be measured easily were related to the blessings and 'curses' a demigod accrued over their time alive. A blessing, or clever 'curse', could make a demigod much stronger than they would be normally, or force them to grow just to survive.
Then there were the innate ones. One being genetic, the closer the child looked to their divine parent the more power they would have. One like this who could easily pass a child version of Poseidon themselves? It was the closest resemblance he could remember.
Then there was an intensity based on the mortal parent. The more the divine parent cared about the mortal parent, the more powerful the demigod would be. If Poseidon cared enough to send two deities to protect the parent and see the child to camp? Deities he had a sinking suspicion were Triton and Amphitrite.
This was a child that could certainly fit the title of 'Child of Prophecy'.
"Greetings young man." He called out, not wanting to say anything before Poseidon had a chance to claim the boy. Dionysus would recognize who this was but that man couldn't be bothered to speak up. And the demigods who'd gone to the Winter Solstice meeting wouldn't recognize him as the gods had specialized appearances for those meetings, different from their usual guises.
"Hello Chiron, trainer of Heroes." The child nodded, a mischievous grin on their face as they stood just outside the boundary, staying in the heavy downpour. But the longer he looked the more he noticed that despite the large raindrops hitting the young man, the demigod was bone dry.
"Are you not going to cross the boundary?" he was confused as the child laughed.
"Thought I'd wait to be invited in first." The child stepped across the boundary, expression mirthful "I am a vampire after all."
"Of course you are." Chiron didn't even bat an eye, used to far worse senses of humor. He had spent thousands of years knowing Apollo after all, "Come, I'll give you the tour." He showed the young man around the camp as they ate some lunch during the tour. He wasn't even surprised when the young man, Perseus, saw Hestia and stopped to talk to his Aunt. He even offered half his lunch to the Hearth goddess and several other deities.
They finished the tour around dinner where he brought the boy to the pavilion, the rest of the camp assembled. He had Perseus move to join the Hermes cabin who informed him of the event they'd be doing and who was leading the team.
He never noticed the eyes of the Athena cabin locking onto the young man, instinctual hate and disgust in their eyes.
-Percy-
Standing by the creek, Percy sighed. The gear they'd given him for this wargame was ill fitting and cumbersome and he honestly wasn't sure if it was simply due to him just arriving that day and the time to properly fit being limited or acts of spite from the Athena Cabin who were leading his team.
He'd felt their hatred the second they laid eyes on him, something that Triton had said was likely to happen.
And he couldn't even use father's birthday present until he was claimed, which sucked.
Continuing to ignore the 'Team Captain' watching nearby under an invisible hat, the shadows letting him know full where she was, Percy gazed out into the trees. He could hear the imminent arrival of the Ares campers before they were visible.
"Hey there Punk." The biggest of the lot sneered, "Names Clarisse. You know, we've got an initiation for newbies here at camp. But you're gonna get something special here."
"Oh goodie." Percy sighed, "Let me guess, you're going to try and beat me up? One on one or are you all going to jump me at once?"
"Oh? Calm one ain't cha?" Clarisse's grin grew wider even as her spear crackled with lightning.
"For now." Percy nodded cryptically, Clarisse's siblings looking confused but the large daughter of Ares just grinned wider.
"You know what newbie, you didn't blubber or bitch so you get the privilege of a one on one with yours truly. Try not to lose too quickly." Clarisse spun her spear around and got into a ready stance.
"This isn't exactly my preferred weapon but I'll do my best to make sure the fight is a good one." Percy readied his sword and shield, subtly sliding his left foot back into the creek as he felt power. The two were frozen before Clarisse charged with a yell, Percy using the leather lined shield to parry away her thrust, his own sword following in the momentum. Clarisse proved her bloodline by striking his blade with her bracer, sending his sword up in a shower of sparks, her lazy grin now a wild and eager one.
"Hah! So, you can already fight." Clarisse threw her knee up as Percy leapt back to avoid the superhumans trike from hitting his chest, "You one of my brothers?"
"No." Percy shook his head with confidence.
"You're quite sure of that." Clarisse noted even as she began doing a flurry of thrusts with her spear, Percy having to dodge or parry at a rapid pace.
"My father told my mother who he was." Percy explained, taking advantage of Clarisse's surprise to strike at her spear with his sword, knocking it from her hands.
"Fucking damn it!" Clarisse cursed, hands up as she glowered at him "Expect me to kick your shit in when we have a rematch newbie. And you won't have that little bomb to shock me into an easy win then either."
Before he could respond, several things occurred at once.
The first was a college age demigod from the Hermes Cabin who he remembered introduced themselves as Luke charged into the clearing with the Ares flag. Clarisse, even captured, ordered her siblings to stop them.
The second was that the weather barrier for the camp failed, a torrential downpour hitting the cloudless valley for the first time since the camp had been moved to the area.
And third, a titanic roar shook the ground as a monster forced its way out of the tree line. A Minotaur, monstrous and wielding an axe covered in trophies from slain demigods.
A monster who's eyes were locked onto Percy's.
He had been calm before, and when asked said he was calm for now. Much like the sea his temperament was prone to change on a dime.
He had been calm before, but now he felt rage.
Roaring back, he leapt at the Minotaur, lightning pouring from his eyes and shadowy miasma rising from his skin as he threw a hard punch as the surprised beast's face. The Minotaur was sent back hard into one of the ancient sturdy trees along the creek's bank, their axe falling to the ground from slackened fingers.
Percy's punches rained down like thunder, each fist crackling with the lightning of the storm bringer and the might of the earth shaker. The demigods and Chiron who'd been converging on the boundary for the conclusion of the game saw the fury of the sea, the power of his bloodlines.
They saw Percy tear the horns from the Minotaur's skull and use them as daggers to kill the beast.
They saw a glow appear above his head.
They saw three tridents appear there, each of his father's forms claiming him, acknowledging him. He held out a hand as the ring on his finger turned into a gleaming trident of his own.
Lightning flashed and the rain poured down as Chiron stammered, eyes locked onto the triple trident. Chiron clearly knew what it meant and wanted to stay silent but couldn't, not with the ancient laws and oaths that bound him to declare any true claiming.
"A-all Hail, Perseus Jackson. Son of Poseidon, the earth Shaker, Storm Bringer, Father of Horses. Son of Neptune, lord of Fresh Water and the Seas, earth shaker and horse father. Son of Poseidaon, first King of the gods, lord of the seas, the underworld, and earthshaker."