~(A/N: This one isn't a reader insert but it's more like an AU fanfiction that takes place around season 5. Also, I haven't read the Percy Jackson series since probably like sixth grade so I'm sorry if this sucks. By the way, this was requested by @Mjb198)~

"Do I smite him?" Castiel eyed the kid who just suddenly appeared at Bobby's house. Sam had tackled him and tied him up to a chair earlier for questioning in the basement.

"No," Dean narrowed his eyes at them, "So who the hell are you and how did you get in here?"

He splashed holy water abruptly on the intruder who was now tied up. The kid flinched but there was no sign of it hurting him.

"Dean, he's not a demon. I would've been able to see his true face if he was," Castiel muttered.

"Then what the hell is he?" Sam interjected.

Castiel shrugged with a worried look on his face, "I'm not exactly sure. He definitely isn't human. Well partly."

"Partly?" Sam raised a brow.

"Can you let me explain?" the kid looked exhausted and annoyed by all the bickering.

"Go right ahead," Dean shrugged, sitting on the edge of the table to wait to hear the brilliant explanation.

"My name's Perseus Jackson. But you can call me Percy. My dad is Poseidon and my mom's human. I'm a demigod," the kid explained.

"Wait a sec- did you just say Poseidon? As in the Greek god of the sea Poseidon?" Sam's eyes widened in shock.

Percy nodded and glanced towards his sleeve which was covered by his grey hoodie, "Look."

Dean eyes him suspiciously as he crept towards him. He slowly slid up the sleeve to reveal a tattoo of a trident on Percy's forearm. "Okay, so what? You've got a cool tattoo. That doesn't change anything," Dean scowled at him.

"Just...watch," was all Percy said in response. His eyes were focused intensely on the knife Dean was holding in his hand. Suddenly, the blade turned into a burst of water that slipped through Dean's hand.

Dean jumped back in shock, "What the hell?!? How'd you do that?!?"

"I told you. I'm a demigod. I can do other stuff too if you want to see,"Percy implied, his lips curled into a smirk.

"I'll pass," Dean shook his head, still in shock from what just happened.

"Can you untie me now? Or do I have to turn this rope into water too?" Percy asked with an arched brow.

Dean hesitated for a moment, giving him his bitchface. Instead, Castiel decided to untie Percy from his restraints. "You still haven't explained how the hell you got into the house," Sam commented.

"I'm not really sure. Apollo told me if I ever had a dream about you three that I needed to find you right away. So I did have the dream and told Hermes, who sent me here and well I...appeared," Percy shrugged.

"Hermes...Apollo...who the heck are all these nut jobs?" Dean furrowed his eyebrows.

"Greek mythology. Try reading a book for once Dean," Sam sighed.

Dean shot Sam a death glare then looked back at Percy, "Okay so why was it so important for you to come see us?"

"Apollo didn't say much. He said something about Lucifer trying to get rid of all the pagan and Greek gods or something like that and told me that you three could probably help," Percy explained.

"Us three? Seriously?" Sam arched his brow in disbelief.

"Yes. I need you to help me find him and stop him," Percy stated.

"That won't exactly be a simple task. Lucifer is quite strong," Castiel explained.

"Please. All these greek, very wrathful, gods and goddesses are counting on me and I'm just a teenager with no clue what I'm doing," Percy pleaded.

"Fine," Dean sighed, "We'll help. Mainly cause we want to stop Lucifer too."

"So how do we find him?" Percy asked with wide green eyes.

"You don't even know where he is?" Dean scowled at him.

"Sorry no," Percy shook his head.

"You've got to be kidding me," Dean muttered in frustration.

~Time Skip~

"Annabeth!" Percy called out as they all ran over to a girl with long honey blonde hair stood chained up against a wall, caked in blood. They'd searched for Lucifer for the past week and this was there closest clue to where he'd be.

"You know her?" Sam asked as he ran over to help unchain her.

"Yeah we're close friends," Percy said, helping her stand up, "Are you okay?"

"Yes I'll be fine. We've got to go like now before he comes back. Where were you?" she snapped at him, regaining her balance.

"Well that was quick," Dean muttered.

"Who the heck are you?" Annabeth eyed Dean suspiciously.

"Dean Winchester. And you should be thanking us for saving you lady," Dean glared back at her with crossed arms.

"Wait- Winchester? That Lucifer guy...he knew you guys would come. You shouldn't be here," she shook her head with wide eyes.

"Wait- are you saying this was all a trap?" Castiel asked with a worried expression.

Suddenly, claps were heard from afar. Everyone turned stiff as they looked to see who it was. "Well done brother," Lucifer clapped as he walked in glancing at the others as well.

"So you're Lucifer," Percy muttered angrily.

"And you must be Poseidon's son. Perseus, is it?" Lucifer asked. Percy huffed in response. "What's with all the third degree everyone? I just want to have a little chat is all."

"We know damn well the last thing you'd want to do is have a 'chat',"Dean scowled, gripping tight onto his blade.

"Common. We're all adults here," Lucifer glanced at Percy and Annabeth, "Well most of us. I just want to post a proposition."

"Oh really? And what's that?" Sam asked.

"Sam can be my vessel and I'll stop killing all the pagan and Greek gods. Seems like a decent deal," Lucifer suggested.

"So you could just kill a bunch of innocent people after? We're not stupid," Dean rolled his eyes.

"Okay," Lucifer flicked his nail, "I guess you'll just have to say goodbye to your father then Percy."

"Wait what? What did you do to my dad?" Percy clenched his jaw in anger.

"Let's just say he's a little wrapped up at the moment," Lucifer smirked.

Percy turned to the Winchesters, waiting for them to do something. "What? We can't let Sam be his vessel. He'll probably still kill your father either way," Dean said.

"Are you serious? It's my dad. Wouldn't you do the same thing for yours?" Percy asked.

"Our dad is dead," Sam said blankly with a serious tone.

"Oh I'm so sorry," Percy apologized.

"You don't have to apologize. You're not the demon who killed him," Sam responded.

"Sorry to interrupt this grieving moment but the clock is ticking Sammy," Lucifer chimed in.

"We may have lost our father, but you shouldn't lose yours," Sam nodded to Percy then took a deep breath, "I'll do it."

"Really?" Everyone else asked in shock.

"Don't do this Sammy. It's not worth it," Dean pleaded.

"I've got to. This needs to stop," Sam said, walking towards Lucifer.

Lucifer smiled in pride, "Are you ready Sam?"

~(A/N: and that's all. I could make a part two if anyone really liked this. And for others, I have been reading your suggestions and I'm working on them, I've just been really busy with traveling and stuff)~