Knowledge needed to read this: MCU and my HOO fanfics.

In an AU where Annabeth dies in the Giant War. Percy, thinking that two of his best friends are dead, not knowing Leo was alive, thinks that the prophecy didn't come true and everything was for a waste, and accidentally winds up in the MCU. He fits in with the Avengers and becomes a secret operative for them, and this is when Thea realizes he's in an alternate universe and goes to get him back.

Nick Fury's POV

I didn't exactly approve of Stark's new base for the Avengers, but he did clean it up nicely, I'll give him that. So when Stark brought an 18-year-old kid to me and told me that he could be useful, I trusted him. Who would have known how useful and powerful he was, and what a mess he would bring with him.

This kid was Percy Jackson. He didn't exist anywhere on the internet, no birth certificate, no family records, nothing. It was like he just appeared out of nowhere, which is what Stark claims that he did. But he was smart, powerful, skilled, a perfect soldier, so I let it slide then, asking Barton and Romanoff to keep an eye on him. Even with their skill-sets, I wasn't sure if Jackson got out of control, we could contain him.

He was a well-built man, and looks Romanoff described as 'cute and scruffy.' He held himself like he was nothing, like he was broken, but he radiated the sense of leadership that Rogers often displayed. There was a fire in his eyes that couldn't be snuffed out. He had a dark hair, tanned skin and unusual sea green eyes. Those definitely weren't natural.

He, like the Maximoff twins, had powers, but his seemed to be ingrained in his DNA, not a result of experimentation. Stark called it hydrokinesis. The ability to manipulation water particles and bend them to his will. He was also capable of talking to fish and equestrian creatures like horses, but despite all these abilities, he had several mental issues.

ADHD and dyslexia. Jackson claimed that the ADHD helped him concentrate in a battle, but I wasn't so sure. After a physical examination, Rogers explained to me that he was as fast as he or any other super soldier was, and although not as strong, he could still hold his own and even beat the Captain.

There was one more thing I found concerning about him. He couldn't be seen on any digital device. When Wilson looked through his visor, he was non-existent. When Stark and Rhodes looked through their interfaces, he was invisible. Not even a heat signature. The digital world seemed to be intent on making him non-existent. Thankfully, this was a perfect ability for a spy, and that was what we trained him to be.

He was a warrior with a fiery heart. We taught him to dim the flames and be icy cold. He was a shining star. We taught him to hide his light and be the soulless dark. It wasn't easy, but we did it.

Even if he refused to tell us his past.

According to Barton, he screamed when he slept. He yelled names in an unknown language and cried when we woke him. His back was covered in scars, and so was the rest of his body. There was so much scar tissue on him, it was unlike anyone else we had seen. Not even Romanoff, a former Russian spy, had as much scars as him.

So when a girl that looked so similar to him, with the same tanned skin and dark hair, managed to evade all security measures and just appear in the cafeteria, we immediately locked her up.

SHIELD protocol.

She had a green leather jacket on, a dark grey top, black leggings and thigh-high heeled boots. A silvery gray shawl was around her neck, and with that look she looked like a normal teenager.

I walked in to the holding room which held her, who didn't even seem surprised with her handcuffs cuffed to the tabletop. "Who are you?"

"The only thing I will say to you is that I will only talk to Percy Jackson." She said, steely calm. When I looked at her now, I realized that her eyes, unlike Jackson's, were silvery. Not gray. Silver. There was still that underlying sea green color to it, but silver at the same time. How was that possible?

"He's busy. You get me." I responded sharply. "Now, who are you?"

"The only thing I will say to you is that I will only talk to Percy Jackson." She said again with a playful smirk.

"For god's sake." I cursed, until Hill's voice buzzed in the earpiece. "I'm interrogating an intruder, Agent Hill, I'm a little busy."

"That's our problem, sir." She answered. "The dark haired girl, right? That's the one you're talking to right?"

"What's your point, Hill?"

"Sir, there's no one but you in the security feed. There's no one there. Just like Perc-"

"I realized she's like him. She's been asking for him. The only thing she will say to me is that she'll only talk to him, and that's the only thing she's going to say. Bring him in. I hope he's not busy."

"He's at the door." A knock came at the steel door, and I stood up to open it. Jackson stood there, and raised his eyebrows curiously.

"Maria sent me." He explained.

"I realized." I answered. I let him in, and he looked at the girl. His face morphed into an expression I had never seen him make. Not even when Thor explained the Norse gods thing to him.

Confusion.

"Hella?"

The girl seemed to smile, but then looked at him with a glance. Jackson nodded, and then looked at me. "She won't talk unless you leave the room. And go to the security room. Also, assemble the Avengers with you. She wants you guys to be there as we talk, so we have some privacy but you guys can still hear."

"You got all that from one glance?" I asked. "Is she a horse in disguise?"

"She speaks horse." He answered sarcastically before I realized it wasn't sarcastic. The girl gave me a pointed glance and gestured me to the door with her eyes. I obliged and spoke into my earpiece.

"Avengers, assemble in the security room. Apparently, we've got a documentary to watch."

It was only when everyone was assembled did the girl start talking, like she knew exactly when everyone was there. "I do." Said the girl in the video. "So, this is actually the Avengers base. Leo will love this."

"Past-tense, Hella." He sighed. "And what's the point of making them watch if they can't see us?"

"They can now." She drummed on the table, and suddenly, they appeared on the screen.

"You didn't- no don't!" Percy cried, and their images flickered, before reappearing steady. "Why would you do that? They can see us now. And when could you-"

"Overpower you? I always could. Just never gave the effort. And not past-tense. He's alive, Perce."

"Of course. That's why you're here. I'm not going back, even if you know how. Who sent you? Jason? Nico?"

"I came here on my own terms. No one knows I'm here. You have to come back, Percy. You can't keep running from it. It's been a year. I gave you a year before I started joining the search effort."

"A year? And I thought you cared."

"Perce I do care. But I also know how it felt, and I shut myself off from everybody else. I thought you needed the same time, so I gave it." She answered. "You have to come. Everyone needs you. You're an inspiration, a hero, an idol."

"A hero saves people." He muttered. "I couldn't save her."

"A hero saves as many people as he or she can. I couldn't save her either."

"But you weren't there. I was right next to her! I could have, but I couldn't! Do you know how that feels?"

"Yes I do! I loved her as much as you do, Perce. Yes, she was the love of your life, but she was my sister as well. But you have to learn that we can't save everyone. And you're not the only one that's hurting."

"Did we know about this?" Stark asked. "That he lost the woman he loved?"

"We knew he lost people," Romanoff answered. "We just didn't know how many."

"I know you guys hurt. But I hurt more. You didn't know her like I did, Thelle. I loved her. I loved her with all my heart. I can't live without her."

"Yet here we are." She stated. "I know how you felt, Perce. I have been in you. I have all your memories when I was tortured. I know your pain, something that no one else knows. I also know that you haven't faced her yet. I asked Nico. You never went to visit. Big Uncle Z said that you were allowed to visit once. But you never took it."

"Did you take it when she died?" He responded.

"Am I the only one who's starting to think they're talking about two different deaths?" Wilson asked suddenly.

"Not the only one. Two deaths. One that hurt Perce, one that hurt Thelle, but they were close with both of them." Hill said. "And they're so young."

"I was that young." Romanoff sighed. "But I was taught to hide emotion. Percy wasn't."

"I wasn't given the chance when I lost her, but I did it anyway. Because I needed to face the fact that she died and I didn't save her. And that I would know who the have my revenge on. I know your fatal flaw, Percy. Loyalty to her wants you to follow her till the end, like when you were on the edge, but loyalty to the rest of us makes you keep on living. So you're stuck on a tightrope and refuse to just fall."

"What if I want to stay there?" He responded. "Stay on the tightrope."

"Then it'll snap and you won't have a choice. And her death will be in vain."

"SHE WAS MY SISTER TOO!" Percy suddenly yelled.

"Who's she?" Rhodes asked.

"From what I'm getting, Thelle's death is their sister, but Percy's death is his girlfriend but Thelle's sister." Romanoff said. "But I still can't tell if any of this is adopted or anything like that."

"You knew her for 9 months!" Thelle had stood up by now, the handcuffs snapped. "I knew her for 15 years! She was my twin sister, Percy. You're only her half-sister. You only knew her for that time. But she was my life!"

"I know how that feels," Wanda muttered softly in the corner, and Vision looked at her with a sigh. Piedro's death still weighed on Wanda heavily.

"Annabeth was my life!" Percy yelled. "But how can I live without her?"

"So she has a name. The girlfriend is called Annabeth." Stark pointed out.

"You've been living for a year in a world you don't belong in without her. And finally, you just back my own point. The brother I knew would never stop fighting, even if you were fighting against the entire world. My brother was a hopeful boy."

"Then what am I now?"

"He's been replaced with a broken man." Thelle said. "Snap out of it. The pain will never go away, but it makes you stronger. You need to move on. Camp needs you."

"What are we against?"

"Our own sorrow and grief. How can we move on, if our leader himself is missing and won't move on?"

"I'm not their leader."

"PERSEUS!" Thelle yelled, her hand slapping down on the table, and the table vaporized into silver dust. "You're not listening to me!"

"His full name is Perseus?" Stark asked in disbelief.

"Did she just vaporize the table with her hand?" Rogers asked instead. "What on earth is wrong with this world nowadays?"

"I am trying!"

"Stop trying, and just do it!"

"How did you do it? How did you continue living when Tori died?"

"We have a second name. Tori's the sister. That's a start in explaining what's going on." Wilson shrugged. "By now I'm completely lost."

"You're not the only one." Rhodes replied.

"Being in a coma helped." Thelle answered. "Destroying the mastermind behind her death in a great fiery explosion also helped. Even if it meant that I would get thrown out of the sky 30 stories above the ground and spend the next 5 months in excruciating pain. But I had the choice to wake up then. I could chose to ignore the pain and just wake up, but it took me 5 months to decide that while in a coma replaying the past 6 years of torture I was put through while trying to avenge her death. Then I got to slice up the traitor into tiny little pieces so that was a bonus."

"Now is not the time for jokes, Thelle!" Percy groaned.

"Why not? That's what you used to do. You could be facing Hyperion and still crack jokes about him as a maple tree, or make bets about drinking Gorgon's blood in order to save your memories. Because that's who you were. You were Perseus Jackson, son of Poseidon, Prince of the Seas, Hero of Olympus, I'm not going to continue with your titles."

"What are all those names?" Wanda asked.

"Greek Mythology." Vision answered. "Perseus is a Greek Hero, and those other things are places or Gods from Greek Mythology."

"The gods of Olympus, the Greek pantheon and equivalent to the Asgardians of Asgard. The Olympians. Those two, they're demigods." A voice rumbled behind us. Thor Odinson, god of thunder. "If they are children of Poseidon, they are as powerful as me."

"As powerful as you?" Wilson repeated. "Damn."

"Perhaps the girl is even more. I always sensed something about Percy, well Perseus, when I met him. Something godly."

"And you're only telling us now?" Stark said.

"I did not see reason to. He was no current threat."

"Why are you even telling me this? You were just my dad cheating on mom after he abandoned us. You shouldn't have been born."

"To be fair, Perce, you were the result of a broken oath from the Second World War when dad decided to cheat on our wonderfully nice step-mom Amphitrite and ended up with you. Did you ever realize when exactly I was conceived? When Sally decided to marry Gabe to save your life. Poseidon couldn't take it, and ended up getting so wasted that he ended up in bed with Tania on her bachelorette party."

"You talk about me letting go of my past. You won't even call your mother mom! You call her Tania!"

"My mother is Athena, she was the one who helped me survive. My mother is Artemis, who gave me the strength to continue. My father is Poseidon, because he gifted me with life. Tania, she was my mortal mother who never even tried to protect me from my so called father. Not everyone had a loving mother like you, Percy. Look at Hazel. Her mother thought she was her curse, and only realized that Hazel was more precious than the jewels she could summon as they died. Look at Luke. Her mother went crazy because of Hermes, baking cookies for a child who would never come back. That is reality, and currently, you are too broken, too fragile, to accept it!"

"How can she say that to him? Percy is no way fragile. He's a better fighter than all of us combined." Rogers said, appalled.

"What if she's better?" I asked, and they looked at me. "What? They're siblings of some sort, they both have hydrokinesis and telepathy, and Jackson just said that she could overpower him."

"She's a lady." Roger protested.

"Like this lady's never kicked your ass." Romanoff retorted, and the women in the room laughed. "But a fight is coming. I can sense it."

"Do we help Perce?" Stark asked.

"I doubt we could do anything." Hill answered. "But I think they can handle it. Thelle just chatted about falling from 30 stories above the ground like it was nothing."

"Can I just say this to you, Agent Maria Hill?" Thelle suddenly said towards the camera, and we glanced back suddenly. We had forgotten she could hear us. "And the rest of you. Stop referring to me as Thelle, that's just what Percy likes to call me since it's different to what everyone else calls me. My name is Arthella Carter, but call me Thea. And falling was a big deal. Just see the scars on my back. They'll make Percy's look like a new-born baby."

"Arthella Dianne Carter, Sylvia Hunter and Dianne Chase." Percy added. "Put all three of those names into the database. She goes by a lot of names these days."

"When you're pronounced dead to the outside world, you need them. Also, when you look like a 16 year old permanently, you need an older alter-ego. A wager, then. If I beat you in a fight, you have to come back with me to Camp. You can come back here if you like your life here, but you have to tell them you're alive. You need to be the face of hope. They don't know who I am anymore. I had to wipe those memories."

"Why?"

"Because I reversed time so that the Night never rose back up to attack us. I am a flaw in the course of time. That is why I can do what I can do. But now the world is back to how it should be, and I know that there's a part of the story that needs you in it."

"Fine. A battle. But you'll have to give me a little disability. No powers."

"I can't do no powers."

"Oh, right. No offensive and defensive powers. And no wings. That counts as a power."

"She has wings? I want wings!" Wilson complained.

"You have wings." Romanoff pointed out.

"But Perce means legit wings, not mechanical wings!"

"Be quiet. Get the training room ready, they'll need it." I interrupted. "We'll set up the room for you two. Are we allowed to watch?"

"Be our guest. Maybe you can learn how a real warrior fights."