I do not own Percy Jackson, Heroes of Olympus, or the Avengers. I hope to write stories that that create a new world, a possible alternate one that cross-overs between these worlds to create a new one.

Author: The Sea's Avenger

Title: The Sea's Avenger

Premise: What would happen if the world of Percy Jackson crossed over with the world of the Avengers? What if there was never a pact of the Big Three? What would happen if Sally Jackson took Poseidon's offer to live under the sea? What if there was never a war against the Titans or one against Gaea and her children? What if Bucky Barnes died in WWII and was never forced to become the Winter Soldier? What new alternate world would arise from such changes? Read and you will see.

Chapter 1: A Father's Oath

Malibu, California

A blonde teenage girl ran through a large kitchen that overlooked the ocean. The wall facing the ocean was a floor to ceiling window; the floor plan of the home was open, but with an inviting feel to the mansion home. The teenager ran through the house with a thick white envelope in her hand. She ran to a wrought iron, circular staircase before she quickly descended toward the basement level of the home. She jumped over the bottom step, landing gracefully on the concrete floor before rushing toward a glass wall with a hand print scanner attached to a glass sliding door. The girl adjusted the envelope into her left hand before she placed her right palm against the scanner; a green light lit up her palm.

"Mister Stark has set the garage to the private setting Miss Stark," a disembodied British voice said from a speaker in the ceiling above the glass door.

"Jarvis come on, I have great news," the girl huffed in frustration.

"Miss Stark, I will check with Mister Stark, to see if he will allow you to enter," Jarvis replied.

The girl stood with her right hand on her hip and her left hand holding the envelope, spinning the envelope in an agitated way, like she couldn't stand still for even the minute or two it would take for Jarvis to convince her father to let her into the garage/workshop.

"Miss Stark, you may enter," Jarvis said before the glass door slid open revealing the inside of the garage. The garage was one large room, nearly the size of a soccer field. The girl looked around, still amazed at all the scientific equipment, the row of ten sports cars, and more importantly to her, the far wall that held ten variations of the Iron Man armor, her father's alter ego. She looked around the room, but her father was nowhere to be seen.

"Dad," the girl yelled after giving up trying to look for her rather eccentric father.

"Princess," a voice yelled, even with a yell the voice was fairly inaudible.

The girl looked around. She bit her upper lip, because gods help her she could not find him. "Where are you?" she yelled, stomping her foot to emphasize that she was not in a good mood.

A soft chuckle could barely be heard from behind her. It came from under a white Bugatti Veyron 16.4 Grand Sport. A pair of leg's dressed in stone wash denim were the only visible signs that a man was under the vehicle. The girl marched over to the man and quickly kicked him in the shin, earning another sound as the man smacked his head against the underside of the two million dollar vehicle. A few choice words later the man slid out from under the vehicle. He wore an AC/DC shirt and his black hair was messy, but his goatee was neatly trimmed. He rubbed his forehead, which now sported a red mark and a grease spot where he hit the oil pan of the vehicle.

"Annabeth Minerva Stark, what in the name of…" Tony stopped talking once he saw the look on his daughter's face. He would have said one of his famous one liners, but he didn't want another kick, possibly somewhere a little more sensitive than his chin. "Okay… Jarvis."

"Yes, Mister Stark"

Tony looked up at the ceiling, wishing that there was something to scowl at when he spoke to Jarvis. "Why didn't you tell me that she was in a mood? It's not that time of the month?" he said, asking the second question in a whisper.

The sound of his daughter clearing her throat broke the billionaire away from his discussion with Jarvis. "Are you done now?"

Tony raised his hands in surrender. Annabeth gave him a look that was both amused and downright scary with those big grey, piercing eyes of hers. Too much like her mother, he thought. He cleared that thought away quickly before he asked, "What was so important that you had to unleash the wrath of the gods on me?"

Annabeth's grey eyes intensified. She held the envelope out in her left hand. Tony looked at it, but he couldn't read the text on it. "You're a delivery girl now?"

Annabeth sighed. She ignored the stupid comment. "It's an admissions letter," she said. Tony's dark brown eyes widened. "To MIT," she finished.

A broad smile stretched across his face before he jumped up to his feet, wiping his oily hands on his jeans. "Well, don't just stand there open it," he exclaimed.

Annabeth huffed. Now he was excited. Leave it to her crazy father to ruin her moment. She sighed before she tore open the envelope. She read the letter quickly before a broad smile stretched across her face. She looked at Tony, a smile forming on his face when he saw her smile. He gave her a look, asking her to confirm what he could only guess was good news. ""I got in," she said.

"Of course you got in," Tony exclaimed. "You're a Stark after all."

Now his daughter's hands were on each hip as the grey eyed glare returned. "And a daughter of Athena."

Tony rolled his eyes. "Yes, of course, bring up your mom at a time like this."

Annabeth closed her eyes and counted down from ten. She wouldn't let her father get to her. "You know, I came down here to have a father and daughter moment, but it turns into just another crazy talk with you."

Tony's smile disappeared. "Sorry?" he asked, like he didn't know what he was apologizing for, which he probably didn't. "But, you're in, I'm so proud of you." He rushed forward and hugged his daughter. However, when he didn't feel her hug back, Tony released her and stepped back, trying to see what was wrong. When he look at her white blouse he saw it, the large black grease stain that now proudly or sinisterly sat in the middle of the shiny white blouse. Annabeth's grey eyes were big, her face was red, but it wasn't from embarrassment. Tony looked at his arm, acting as if a watch was there. "Oh look at that, I have a thing, with Pepper," he began, realizing that he wasn't wearing a watch. "Yeah, a thing with Pepper." He turned and ran to the nearest car, which just happened to be a red Ferrari F12 Berlinetta, he opened the door slid into the seat behind the wheel, starting the engine with a roar before he sped out of the garage. Jarvis opened the door just in time to let the car escape before it scraped the beautiful and very expensive car's top.

Annabeth stood looking at where her father had been before a scream echoed out of the house and down the driveway. A scream that made Tony flinch as he raced away. He cringed thinking about what was going to happen to him when he returned in the evening. "Jarvis," Tony said.

"Yes, Mister Stark," Jarvis replied.

"Remind me to buy her a new architecture book."

"Sir, do you believe that will be enough?"

Tony thought that over as he pulled his sports car onto the main highway. "Yeah, you're right, please have my contract attorney contact Architect Magazine." "Yes sir, what should I tell him about the nature of the issue?" Jarvis replied. Tony grinned. "Tell him to buy the magazine."

Atlantis, Southern Atlantic Ocean, five hundred miles from the continent of Antarctica

A dark haired women with piercing blue eyes and blue skin peered out a window in the great palace of Atlantis. She looked down at the garden below that was filled with ocean plants and sea life. Sitting on the tiled mosaic floor of the garden walkway was a teenage boy of fifteen years old, now sixteen. He was tall for his age, roughly six feet two inches in height. His skin was the color of the surface dwellers and tan from many an hour floating on the surface in the sun. He had pointy ears like any other merman, but that is where the similarities stopped. He had legs like the surface dwellers, but his hands and feet were webbed between the fingers and toes. The boy's jet black hair that was long and messy, but his eyes were the most unique aspect of the boy. His eyes were sea green and they glowed in the low light of the undersea garden. He wore a pair of denim pants, which seemed to make him itch because he wasn't used to them. He had a blue shirt with a gold trident on it, in honor of his father.

"Sally, what's wrong?" a strong voice asked from behind the woman. Sally turned, her fish tail whipping below her in order to move her toward the sound of her husband, Poseidon; the god of the sea and King of Atlantis. "Poseidon, I see our son down there, he's so alone," she replied sadly.

Poseidon sighed, bubbles moving through the water. "This is my fault. I knew I should have waited. We should have been married before we had a child. I knew that the transformation would have side effects since you were pregnant at the time."

Sally reached out and took his hand. "It's not your fault. We fell in love and you were at war, with Oceanus, Amphitrite and Triton. You needed me and I was there."

Poseidon nodded before smiling as he looked at his beautiful wife, remembering when she was just a human, a legacy of Jupiter himself. His smile faded as he remembered what the day was, the 18th of August, Perseus's birthday. "It is the day," he reminded.

Sally's wistful smile ebbed. "He asks too much of us, too much of our son."

Poseidon nodded. "Yes, but I made a promise. Zeus allowed me a divorce from Amphitrite and he allowed me to transform you and marry you. I cannot go back on that promise."

"I know, but to ask our son to take such an oath, to leave Atlantis and walk amongst the surface dwellers, all alone," Sally said. She looked down toward the ground. "I don't want him to go."

Poseidon leaned forward and pulled her into a tight embrace. "Sally, my queen, we knew this day would come. Perseus is of both worlds. He's meant to live in both. My brother is right, he needs to discover the surface world. He can be a part of both."

Sally looked up at her husband before pulling him into a kiss. "Athena calls you a fool. She doesn't know the wise god that I do."

Poseidon chuckled. "Let my little niece hold to her hubris, it will be her downfall."

Sally slapped him on the arm playfully. "She is family Poseidon. We don't give up on them, even if they act holier than all."

Poseidon chuckled. "Will you come with me to Olympus?"

Sally shook her head as she pulled away from the embrace. "I wish to say goodbye to my son, alone," she said determinedly. Poseidon nodded reluctantly, watching as Sally swam out of the palace toward their son. Perseus, or Percy as he allowed his childhood friends to call him stood when he saw his mother. Poseidon watched them talk for a few minutes before Sally pulled the boy into a tight hug. Poseidon could see her holding back her tears to no avail. A few moments later Sally swam off, away from the Palace toward the temple of Pontus and Thalassa, the great primordials of the seas and the godly godparents of Perseus.

A few minutes later Percy entered the throne room of Atlantis, his father hovered in place, his fish tail keeping him afloat as he waited for his son. A golden glow engulfed Poseidon before his tail turned into two powerful legs. "Are you ready my son?"

Percy looked at his father. "Yes father," he said quietly and sadly.

Poseidon smiled. "Do not worry my boy. You shall enjoy your time on the surface, it is a part of you, a part that you need to learn and embrace."

Percy raised his head and stared into his father's eyes. Poseidon could see the determination, it reminded him of Sally. "I will father. I won't let you or mother down."

Mount Olympus – The throne room of the Olympian council

A golden light appeared in the middle of the throne room. Poseidon and Perseus stood before the council of twelve. Poseidon squeezed his son's shoulder before letting go and walking to his throne and sitting down. A dark haired man with electric blue eyes sat on his throne. He was at his godly height of 15 feet like the other eleven gods in the room.

"I call this council meeting to order," Zeus proclaimed.

"Now to the reason we are here today. Poseidon, please introduce our guest," Zeus said, looking at Perseus curiously.

Poseidon stared at his brother. He suspected that Zeus would be paranoid that his son would try to overthrow him or some other crazy idea, but Zeus looked curious and nothing else. "May I introduce my son Perseus, prince of Atlantis."

Perseus bowed his head at his father and then toward Zeus. "My Lord," he said with another deep bow toward Zeus before he addressed the rest of the council. "It is my honor to be here today."

Athena's eyebrow raised at the boy's voice. He was incredibly polite, but she could also sense intelligence. Maybe the stories of Queen Sally were true, the stories of her intelligence were only equaled by the stories of her kindness. Athena wished Hera was more like the new queen of the seas. "Father, may I address the prince?" Athena asked, earning a curious look from Poseidon and a few others on the council.

Zeus nodded. "Go ahead my dear."

Athena smiled. "Prince Perseus, why are you here today."

Perseus smiled in return. "To fulfill an oath that my father gave to Lord Zeus many years ago."

Athena looked toward Zeus questioningly. Zeus nodded before he cleared his throat. "Roughly sixteen years ago Poseidon came to me and informed me that Amphitrite and Triton had joined forces with Oceanus to oppose my brother's reign as king of Atlantis. Poseidon asked me to approve a divorce from Amphitrite and to remove Triton from his place as Poseidon's heir. He also wanted me to approve of his choice for queen, Lady Sally. I approved as long as Sally and Perseus swore an oath to remain faithful to Olympus and that Perseus spend time on the surface, learning the ways of the people here."

Poseidon nodded. "Sally gave her oath as all of you know, but we had to wait for Perseus to reach age. He turned sixteen today and he is ready to swear his oath and to begin his journey on the surface."

"Perseus, step forward," Zeus ordered. Perseus stepped forward quickly. "Swear an oath on the Styx to remain faithful to Olympus."

Perseus cleared his throat. "I swear upon the Styx that I will remain faithful to Olympus and I shall protect it and the world from all that threaten it." Thunder erupted overhead sealing the oath. Perseus stepped back and bowed once again toward Zeus.

Zeus smiled. "I know that Sally is a legacy of Jupiter, my Roman counterpart; therefore, I wish to give you a gift my boy."

Poseidon stared at his brother in wonder. Perseus stepped toward his uncle. "Yes, my lord, I would be honored to accept such a gift from the King of the gods," he said before he knelt on one knee before his uncle's throne. Zeus smiled at the gesture. He shot a beam of light that engulfed the son of Poseidon before wings erupted from each side of the boy's feet. "You will now be able to fly within my domain. It is unusual for me to give such a gift to a child of my brother, but since you are my legacy as well and you have sworn to protect not only Olympus, but the Earth, I grant you this ability. I hope it serves you well my boy. The wings can disappear on your mental command. I wouldn't want to the mortals to see them."

Perseus nodded before he stood up. The wings flapped a little elevating the boy a few feet off the ground. The wings stopped flapping and Perseus settled back on the marble floor of the throne room.

"Now, where will you go on your adventure in the surface world?" Zeus questioned.

Poseidon smiled. "My son has received early entry into the mortal university, MIT."

Athena's grey eyes widened. "What will be your major, young Perseus?"

Percy smiled. "I have a triple major in Oceanography, Geophysics, and Geology."

Athena's grey eyes widened even more. "He certainly does not take after barnacle Beard."

Perseus hid his chuckle as Poseidon glared at the goddess. "He takes after his mother, Owl Head," Poseidon replied, but he couldn't hide the anger evident in his voice.

Athena smirked at the name. "I would assume," she replied.

Zeus cleared his throat before the two could muster a long and very drawn out argument. "Yes, Perseus good luck with your schooling, council dismissed."

The council all disappeared in a golden light, except for Poseidon. He shrunk down to mortal size and approached his son. "You did well my boy," he said.

Perseus smiled. "Thank you father."

"Now, let us get you settled into school. I also need to show you to your dorm room. I hear you will be sharing it with a demigod. I believe he is a son of Hephaestus."

"What is his name?"

"Valdez, Leo Valdez, I believe that is the boy's name."

Author's Note: I hope everyone enjoyed the beginning of this story. Certainly some mix and matching going on and certainly as an alternate universe I'm taking some liberties with the characters, so they won't be the same. Perseus being the most obvious change. Perseus or Percy in this story will be taking over for Namor in classic Marvel comics. So, you know in the future he will be called the Submariner, so be prepared for that and also to the extent of his powers and how they might differ from Percy and from Namor.