AN: So, we know Athena isn't really all that big on consent in canon. The children of Athena are all born from her mind meaning there's no actual intercourse involved (Virgin goddess) but given that Annabeth's dad was apparently not expecting it and stated he didn't want a kid at that point in his life, it's clear that Athena doesn't ask for consent or for their opinions before making these mind babies and saying 'go raise this kid now and I'm not going to help'. We also know that she is drawn to those who have a creative spark and if it's from the mind then genders wouldn't really matter.

Thus, this chaotic idea was born.

Two Parts god, One Part Man (first look)

-Poseidon-

Using magic to silent his roaring stomach, Poseidon tried not to let his hunger show as the meeting droned on. After his time with Sally and he'd realized she was carrying his child, something he'd sworn he'd set up precautions against, he'd panicked.

This child would be born outside of an oath and he didn't want his child to suffer for his actions.

So he'd gone to Styx, sworn to abide by the old punishment with the alteration of extending the period he was forced to go without nectar and ambrosia in exchange for not being exiled from the council of gods. He couldn't let Zeus figure out what was going on or the bastard would murder his son, regardless of Poseidon taking the punishment for breaking the oath. Styx had agreed, possibly out of shock that an Olympian was actually accepting their punishment and not trying to run. So, for the last few months he'd been going without the food or drink of the gods, and it was agonizing.

He was just starting to wonder if mortal food could possibly quell his divine hunger when the Fates appeared in a thunderous crash. Their faces were far from pleased. Zeus looked ready to grovel, eager to quell their wrath lest it be turned on him, when the trio of ancient deities turned their glares on a surprised Athena.

"Interloper." Atropos, the cutter of the thread, glared at the reeling Wisdom goddess, "Do you realize what you have done?!"

"I…I don't…" Athena stuttered, at a genuine loss for words as Hestia approached the three Fates, unafraid.

"What has my niece done to earn your wrath?" Hestia asked calmly, bringing the attention of the three onto herself.

"She has interfered in our plans, shattered the vision of Fate with a single impulsive action!" Clotho snarled, "We carefully watched, we measured, we readied for the arrival of the Hero of the Great Prophecy. But now, the Great Prophecy has been shattered and we have no guide!"

"If…if the Great Prophecy is broken wouldn't that simply mean that Olympus is safe?" Zeus asked hesitantly before flinching back at the look the three Fates gave him.

"No, whatever was going to threaten Olympus will still happen." Apollo spoke up, unusually serious "But now we lack any sort of guide of what to expect."

"But…how?" Artemis looked baffled.

"By her acting as she always has." Lachesis sneered at Athena "By picking a Mortal and forcing a child of thought. Only this time, she picked someone who was already pregnant."

"Your divine essence, instead of pulling in the woman's mortal spark, was pulled into the forming child." Atropos glared "The already forming demigod, the Hero of the Great Prophecy."

"So…did it overwrite the kid or…?" Ares scratched their head confused as Poseidon realized just who they were talking about.

"The child is now two thirds god, one third mortal." Clotho shook their head, "And unbound by Fate. We cannot see his future, nor can any oracle." An ability he knew that the Fates sometimes gave to Mortals when bored but apparently the chaotic actions of his rival had forced it this time.

"All our work, ruined." Atropos sighed as Poseidon narrowed his eyes at that bit.

"Your work?" He questioned, an idea forming in the back of his mind.

"We had to ensure that the Hero would be born, despite their father's attempts at contraception." Atropos admitted their actions without a shred of guilt as Poseidon fought down his rage. He was suffering this punishment, his oath had been broken, because of their machinations?!

He felt Nyx's presence in the back of his mind, the goddess of hatred soothing his fury as he felt her punishment that bound him vanish. If the breaking of the oath was caused by the interference of others, then the punishment belonged to them.

Regardless, his son was in for a turbulent time.

AN: So yeah, Percy is the of Sally Jackson, Poseidon, and Athena. Two thirds god, one third human, much like Gilgamesh was. Not sure if I'll keep the 'you shattered fate you imbeciles!' or not but Percy would definitely be in for a chaotic time with a much different power set.