Five Times Percy Didn't Adult and the One Time He Did

Two: Poseidon

Peanuts wouldn't be a problem under the sea. It wasn't like they grew in Atlantis- Percy was almost a hundred percent sure of that fact. If he told Poseidon, he'd have to deal with the god checking every single food over and over again, and Percy was a guest at the palace. He didn't want to cause any trouble. Amphitrite and Triton already weren't fans of his and Poseidon coddling him would do nothing to help his case.
He brought an epipen (more like Annabeth made sure he did) but he was confident that a week in Atlantis wouldn't kill him. His mom agreed, and that was good enough for Percy.
He did his own detective work in the kitchens (and made friends with all the cooks while at it- free food, anyone?) because Annabeth wouldn't stop IMing him about him and the risk of getting caught in one of those conversations by Poseidon was getting too high- he found it was safe (they had been confused about what he'd meant and explaining what a peanut was had been the hardest conversation Percy ever had). He'd been correct when he guessed peanuts didn't exist under the sea. It was now his favourite place.
He was also very ready to brag to Annabeth about being right for once.
Five days went by and Percy was confident that it would all be fine- he even stopped carrying his epipen in his pocket because if peanuts didn't exist, why carry it with him? He left it in a drawer in his room and almost completely forgot about it. It was nice not to have to worry about ingredient labels every time he wanted a snack.
Poseidon surprised him one evening. He'd wrangled Amphitrite and Triton into a family night with him and Percy. The god had the biggest meal Percy had ever seen set out on a table and tried his best to keep a conversation going.
Percy studiously avoided looking at their glares throughout dinner, instead focusing on his food and blocking out their voices. He knew they'd have plenty of passive aggressive comments to make tonight, and while they didn't normally bother him, it was his last night in Atlantis and he wanted it to go well.
The Fates must have heard him and laughed, he thought later. No rest for Jackson.
The table was tense and Poseidon knew it. He pulled a bag- a mortal superstore bag, Percy realized- out of nowhere.
"I brought chocolate bars?" He offered, sounding slightly unsure.
They were European, it turned out, which made Percy laugh (and Poseidon's eyes glittered with happiness at the noise). He didn't recognize any of the brand names so he picked a random one and waited while Poseidon cajoled his wife into picking one, too. Triton refused completely- and eventually, Poseidon gave up trying.
Percy didn't check the label; he'd gotten too used to the safety of the seas and the thought to do so never crossed his mind. Nor did he realize his mistake until he was already swimming back to his room for the night.
It had been an hour and half and he was surprised when he started feeling off. It was way too late for a reaction.
Except his head was swimming and his throat felt numb and breathing in water wasn't supposed to be this difficult. He sat down in the middle of the hallway, putting his head between his knees and gasping.
The water, he realized. It had been trying to heal him but now it couldn't keep up with the attack on his body.
Oh, he was going to hear it from Annabeth- and then everything faded to black.