(Disclaimer: I own neither Ben 10 nor Percy Jackson and the Olympians
Growing up, my favorite cartoon was Ben 10 and my favorite book series was Percy Jackson. Because of that, I've always wanted to see a good crossover fanfic with the two meeting and have decided to do so myself! Enjoy!
Timeline wise, this story takes place after Blood of Olympus and after an alternate version of Ultimate Alien where Ben's secret identity is still intact.)
Ben 10: Mythalien or Percy Jackson and the Alien Hero
It was a nice warm summer day in New York city, cars were humming, birds were chirping, New Yorkers were being their usual pleasant selves (not), and one Percy Jackson was having the time of his life.
"I can't believe there hasn't been a single monster attack in two weeks!" He thought. "Maybe the Fates have finally run out of ideas on how to make me miserable! Maybe not, but a demigod can only hope."
Normally Percy would fret over jinxing himself just now, but he had every reason to be ecstatic. Almost a year ago, he and his friends managed to defeat the Earth mother herself, Gaea, as well as her giant offspring. Ever since that final battle, monster attacks had been down by 85%, at least according to Annabeth.
"Ahh, Annabeth." Percy thought. Now that things had calmed down, Percy and his girlfriend had been busy planning on how the both of them would be going to college. As a matter of fact, he was on his way to pick her up for their date.
"PERCY!"
All of a sudden, Percy heard his name being called, disrupting his reverie. He turned around to find his father, Poseidon, in an Iris message.
"Oh hi dad, what's up?" Percy asked after getting over his shock.
"Percy, my son, there is a grave matter we must discuss." Poseidon responded grimly.
"What's wrong?" Percy asked, confused. After everything he and his friends had gone through last year, he couldn't imagine what could be grave enough to warrant a visit from his father. Gods weren't exactly close to their demigod children, and while Percy and his father had a better relationship than most, his appearance out of nowhere was still puzzling.
"Over the last month, sea creatures from my court have been disappearing, every search party I have sent has disappeared as well, those whose bodies have been recovered show signs of having been…changed. I'm asking you to look into what's happening, we've been able to narrow the source down to a warehouse by the docks, but I believe only a half-blood can get to the bottom of this."
"You know if you wanted to see me, you could have just said so!" Percy responded.
"Son, I am being serious, I know after everything you've done you more than deserve a rest, but these disappearances are becoming concerning."
"Say no more dad, where's this warehouse I'm supposed to find? I still have time before I have to meet with Annabeth for our date."
An hour later, Percy arrived at the warehouse. While on the outside it didn't look too impressive or out of the ordinary, Percy had learned that warehouses can house fiendish things… like the fact that Amazon was really a front for THE Amazons who were in the process of planning world domination through online shopping!
But that was not what Percy found on the inside, no. As he entered he saw what looked like a massive ray gun straight out of one of those cheap 50s sci fi movies his mom would rent for them when he was a kid.
Before he could so much as utter: "What the Hades?" He noticed two tanks of sea creatures. One was filled with normal looking fish all shouting at him:
"It's the sea god's son!"
"Free us Lord!"
"Do you have a moment to talk about our lord and destructor Cthulhu?"
You know, the usual stuff fish always said to him since he could understand them, being Poseidon's son and all.
But it was what was in the other tank that horrified Percy, all the fish inside could barely be considered fish, they looked more like freakish amalgams of sharks, octopodes, and crabs. On the side of the tank was a single sign labeled: "Ben Tennyson's DOOM HAHAHAHAHA!"
"Who the Hades is Ben Tennyson?" Percy wondered out loud.
"Only my greatest ENEMY, trespasser!" came a maniacal voice behind the demigod. Percy responded by quickly uncapping Riptide and slashing behind him only for the sword to pass through a hunched sickly-looking old man with red goggles.
"A holographic sword?!" the man scoffed. "How useful! NOT!"
"He's mortal and yet he can see my sword" Percy thought to himself. "He must be one of those few mortals who can see through the mist, like my mom or Rachel!"
"Who are you?" Percy demanded.
"I should ask the same of you boy! But no matter, I shall indulge you, I am Dr. Aloysius James Animo! The greatest animal geneticist who has ever lived!"
"So you're the one turning these fish into freakshows! You're a monster!"
"What are you, from Greenpeace? I am creating a new world order where my glorious creations will be the dominant form of life! With me as their ruler!" Animo ranted maniacally.
"Oh gods, this guy's insane!" Percy thought. "He's not a monster or a demigod, just a normal mortal! What should I do? It's not like I can kill him!" Chiron had always taught Percy never to use his powers as a demigod on a mortal. "It's not like with monsters where they can just come back. If I kill this guy, he'd be perma-dead, can I really make that choice?" He asked himself.
While Percy was debating the merits of just killing the guy, Animo had made his way to his massive ray gun and trained it on the demigod.
"Now you shall be the first of a new species!" he shouted as he fired the ray. Percy tried to dodge, but the beam followed him and zapped him head on. Nothing happened, Percy just got back up and dusted himself off.
"Interesting!" the mad scientist exclaimed as he poured over readouts coming from the ray-gun's control panel. According to my transmodulator, there is something anomalous in your genetic structure that is shielding you from the effects of my ray. Pity. Even though I can't bring you a new life. I shall have fun extracting the secret of your immunity from you, even if I have to tear every gene of yours apart!
"Not so fast Dr. Quack!" came a raspy voice. Both Animo and Percy looked up to see what looked like a red flying Manta ray dart into the warehouse. "I'm about to rain on your parade, Animo!" the creature said as it fired what looked like lasers from its eyes that completely wrecked the 'Transmodulator'.
"CURSE YOU BEN TENNYSON!" yelled Animo as he fell off the fried Transmodulator and onto his back.
"Yeah yeah, let's get this over with, Sumo Slammers is on at 8!" The Manta-ray snarked before hitting a disc on its chest, glowing bright green briefly before turning into a giant dinosaur-man. "HUMUNGOUSAUR" the dino-man yelled as he began to trash the transmodulator.
Before he could make much headway there though, Ben felt a ticklish sensation across his body, when he turned around, he saw a guy with black hair and green eyes swiping a holographic sword at his body.
"Oh come on!" Percy yelled. "The Animo guy I can understand, but this guy's clearly a monster, why aren't you working!"
"Dude, what are you doing?" Humongousaur asked, confused as to why this random guy was swinging a cosplay sword at him.
Percy stopped what he was doing to take a breath, and was about to say something when Animo reminded them that he was still there.
"Fools!, It's like my grandfather always said: 'Never turn your back on an Animo!'" he proclaimed before pressing a button that electrified the floor. Now Percy had plenty of experience getting blasted by electricity, but this was too much, even for him. The last thing he saw before passing out was the dino-man, apparently named: "Humungousaur", falling with a thud and emitting a green light.
When Percy next awoke, he found himself tied up in a sealed room on what he knew innately was a ship leaving New York. "Thanks dad!" He thought sardonically. In addition to his ability to control water, Percy had also inherited control over ships from Poseidon as well as a mental GPS that only works when he's on the water.
Once he shrugged off his grogginess he laughed. "Of all the places that quack could have trapped me, it had to be on a ship!"
"Glad you're having a great time!" muttered a sarcastic voice.
Percy turned and noticed he was not alone, on the opposite side of the room was someone else who was tied up. The only difference was that he had a crudely built clamp over his left wrist. The mystery guy wore a green jacket with a number 10 on the side and had light brown hair and green eyes. But they were not the same green as Percy's eyes, sea green, no, his were more like a green you would expect from a canister of toxic waste knocked over.
"I'm guessing you're…" he began.
"-the guy you tried to slash with a holographic sword? Yes." He interrupted.
"It's not a hologram! How were you even able to see that it was a sword!"
"What are you talking about dude?! It was clearly a sword!"
"Great! It's just like Rachel all over again!" Percy thought miserably.
"Now if you're excuse me, I have some butt-kicking to do with a certain mad scientist." His fellow captive said as he struggled with his ropes.
"Yeah we met!" Percy retorted. "What's that guy's deal anyway?"
"Oh, he used to be a veterinarian before he was disqualified for an award he wanted. As it turned out, he had been conducting twisted experiments on animals. He lost his mind not too long afterward."
"Ah… that's something." Percy replied, but in his mind he was thinking: "I could be having dinner with Wise girl right now but noooo, I just had to do a favor for my dad and now I'm stuck dealing with whatever this is! Why did I have to say the Fates were out of ideas, of course they would take that as a challenge!"
The mystery teen continued talking: "So I know why I'm here, but why are you?"
"I found out… from a reliable source, that certain species of marine life were going missing and I managed to track the source of the disappearances to that warehouse." He started.
"Oh I get it!"
"You do?"
"Yeah, you're from Greenpeace!"
Percy felt his eye twitch. "No, I am not from Greenpeace! Why is that the first… oh nevermind!"
Percy suddenly noticed a leaky pipe nearby, from that he got an idea, he could manipulate the water in that pipe and use it to soak his ropes, then he could control that water and by extension the rope itself to free himself.
But then he realized: "This guy can see through the mist, there's no way I can play this off, unless…"
"Where exactly is this Animo guy now?"
"He's probably busy rebuilding his transmodulator, once done he'll probably drag us into his lab, gloat about how he's creating a new world order and try to turn us into his freakish creatures."
"How long will that take?"
"Hours, I did trash his mutant ray pretty well."
"Okay…" he started, "I'm going to do something that will get us free, and it might require some explaining afterward, so try not to be too shocked."
The other teen scoffed, "Whatever dude, believe it or not, I've seen some things. I also don't think I caught your name."
"I didn't throw it." Percy rebuked, but then relented. "My name's Percy Jackson."
"Ben Tennyson." He responded, introducing himself.
"Ha, you're the guy this was set up for?"
"Yeah, Animo and I have been enemies for a while." Ben answered. "So what are you going to do to get us out of here?"
Percy smirked, "watch." He proceeded to summon the water from the nearby pipe to soak his ropes, then he carefully manipulated said water to untie the ropes. Within no time at all, Percy was free. He walked over and began untying Ben.
"Woah, how did you do that?" Ben inquired as he pried off the clamp on his wrist, revealing a bizarre watch with the same hourglass symbol that was on both of the creatures before.
Percy hesitated. After all, revealing the mythological world to a mortal can be dangerous. But then he remembered that clear-sighted mortals, like Ben clearly was, usually go insane from not understanding what they're seeing.
Also worth considering is the fact that Ben had been a flying Manta ray and a dinosaur earlier, so obviously he wasn't normal either.
Percy sighed to himself, "I hope Zeus doesn't blast me for this."
He finished untying Ben and asked: "How familiar are you with Greek mythology?"
"Not much, I think we covered it briefly in 6th grade, what's that got to do with anything?" Ben asked, confused.
"It's true, all of it, the gods of Olympus exist, and every once in a while they get the hots for some mortal and have kids with them called demigods or half-bloods. I'm a demigod, my father is Poseidon, god of the seas." Percy explained quickly, not allowing any interruptions.
"So that's how you're able to control water?" Ben asked, apparently not phased at all by this massive bombshell.
"Yes, you're weirdly okay with this, by the way."
"Like I said, I've seen some things" Ben answered.
Percy reached into his pocket and pulled out Riptide. "Do you see this?"
"A pen?" Ben asked.
"Well yes, but also-" he pulled the cap off allowing the pen to transform into a sword.
"Hey, that's the holographic sword you tried to stab Humungousaur with!"
"Will you please stop calling it that! This is celestial bronze, it's only supposed to work on demigods like myself or monsters, basically anything mythological!"
"But it passed through me." Ben stated.
"Exactly, it's not supposed to harm mortals! And since you didn't get seriously cut, then you can't be a demigod and if you're not a demigod, then you must be something else entirely. I'm guessing you use that watch to turn into monsters." Percy said, remembering Ben slamming his watch before becoming that freaky dino-man.
"It's called the Omnitrix, and no I don't turn into monsters-I turn into aliens!" Ben corrected.
"Aliens? Seriously? Aliens are real?" Percy responded shocked.
Ben quirked up an eyebrow. "You just told me you're the son of a Greek god, and you find ALIENS unbelievable?"
"Well, when you put it that way, it does sound pretty stupid, creature feature." Percy retorted.
"Ugh! Seriously dude? Creature feature?"
"Eh, nicknames are a big thing where I'm from, you have no idea." Percy laughed while thinking of all the times his girlfriend Annabeth had called him 'seaweed brain' or when his cousin Thalia called him 'kelp head'.
"So what next?" Ben inquired.
"What's next is damage control!" said a booming female voice as a woman holding a torch appeared before the two teens.
"Lady Hecate!" Percy shouted.
"Lady who?" Ben asked, confused.
"Hecate is the Greek goddess of magic." Percy explained.
"Ah, makes sense." Ben replied. "Wait, if you're the goddess of magic you wouldn't happen to be familiar with Ledgerdomain would you."
"I am, but that is not important right now!" Hecate replied. "What is important is that we take steps to avoid complete disaster!"
"What do you mean?" Percy asked.
"Jackson, have you ever wondered how the mist accomplishes its task?" Hecate asked.
"The what now?" Ben asked, confused.
"The mist is this magical veil of sorts that covers up the mythological, it's supposed to keep mortals from seeing what's really happening, and to answer your question Hecate, I always thought it helps mortals fit what they're seeing with their version of reality."
"Precisely! 'With their version of reality', the mist works best on those with mundane worldviews, those for whom the fantastical is unthinkable! That's why Tennyson here is so dangerous!" She said while pointing at Ben.
"Woah, how am I dangerous? I'm just a guy who found an alien watch that's basically a genetic library." Ben defended himself.
"Yeah Hecate, I'm not seeing where you're going with this." Percy argued.
"It is what he represents that's so dangerous! Ever since he found that device 7 years ago, the number of visitors our world has received has skyrocketed!"
"Yeah so?" Ben challenged.
"The more mortals who find out about alien life, the more open minded they will become and the less of a hold the mist will have over their minds."
Percy's eyes widened. "Oh that's bad! Are you saying it could result in the god's existence being revealed?"
"That is precisely what I'm saying. The moment that thing fell from the sky-" she gestured to the Omnitrix. "- I realized the danger of what it represented, especially on the wrist of a child obsessed with using it to help others!"
"If you're expecting me to apologize for helping people, you're out of luck lady." Ben asserted.
"Nor do I expect you to, whether I like it or not, you now serve an essential purpose. Back in the old days demigods, like Perseus here, were the primary protectors of humankind, but since we gods have gone into hiding, our children are now wholly focused on fighting monsters and staying alive. Your activities, regardless of the headaches they cause me, are an important defense against even worse visitors."
"So what do we do now?" Percy asked.
"You know, when I heard that Animo was up to his old tricks, I expected to just swoop in, beat him up, and take him back to jail in time for sumo slammers. What I did not expect today was to find out that not only do greek gods exist, but that they regularly have super-powered children whose secrecy is… somehow affected by my attracting alien activity to Earth! Great, just great!" Ben griped.
"Oh please, I was on my way to a date with my girlfriend, when all of a sudden my dad just randomly messages me that sea life was disappearing and that I should look into it! Believe it or not, creature feature, I was not expecting the major bombshell that aliens exist and there's a guy that turns into them!" Percy countered.
"Oh yeah, well I-" Ben started.
"Silence, both of you!" Hecate boomed. "This is not an ideal situation, but perhaps we can make it work to our advantage!" She offered.
"What do you mean?" The two heroes responded simultaneously.
"Tennyson, I'm not sure if your allies have ever told you this, but you are absolutely awful at keeping your identity secret! There have been many times I have had to extend the mist to prevent some of your more audacious shenanigans from compromising everything!"
"Like what?" Ben asked.
"Like that time you crashed an alien ship into the ocean!"
"You did what?!" Percy shouted, not happy that the ocean was hurt.
"Oh, like I had any control over where Vilgax's ship crashed!" Ben countered.
"Or that time that dreadful Ectonurite enemy of yours managed to enslave everyone on the planet by turning them into radioactive zombies!"
"When did THAT happen?!" Percy asked, shocked.
"Remember 7 years ago when everyone suddenly woke up not being able to remember the last 15 minutes and all the world's governments claimed it was a clock error caused by a solar flare?" Hecate asked.
"That was YOU?" Percy turned on Ben.
"Technically it was Zs'skayr's fault, but that's not the point! Getting us back on track from my greatest hits, how do you suggest we make this work to our advantage!"
"Simple, for better or worse you two know about the other's side of the world. I could erase your memories but then we would have the same problem all over again. Therefore, the only workable solution is that you must work together from now on to prevent further catastrophe." She finished explaining.
"Well I mean, I guess it could work." Percy conceded. "I bet if we get Annabeth to help us, our 'alliance' would be more effective."
"My cousin is pretty much a sorceress so she could help too!" Ben suggested.
"No no no no no!" Hecate practically shouted while facepalming. "NO one else can know about this, what we have talked about can never leave this room, it is too much of a security risk!"
"But Hecate, Annabeth's a daughter of Athena, I can think of no one else who would be excited about the prospect of alien life!"
"That's the problem, this isn't something to be excited about! What we are attempting is dangerous, and can drastically affect our world!" She lectured Percy.
"And you!" She said, turning to Ben. "If you so much as breathe a word of this to any other mortals, including that upstart cousin of yours, I will personally feed you to my incontinent pet weasel."
"Yes ma'am!" Ben panicked.
"Good, now that we are clear on this issue, I sense this Animo person has finished rebuilding his device. As a trial run of this collaboration of ours, you must work together to stop him. Tennyson I assume you have access to a species capable of getting the two of you out of here?"
"Yes!" Ben answered quickly.
"Good, I leave you to it!" As soon as she finished talking, she vanished in a brilliant flash of light.
Percy and Ben stood there blinking at each other for a few minutes while they processed everything that had happened. Once done it was Percy who broke the silence.
"So that alien of yours?" He asked.
"Oh right!" Ben responded as he manipulated the watch on his wrist. Percy was then blown away by how the dial seemed to rise from the frame as if it were bigger on the inside. He was even more fascinated by the holograms that projected from the dial, taking the shape of creatures he had never imagined.
One was the mantaray from earlier, another was a four armed behemoth, followed by a creature that seemed to be made out of rocks.
"So these are all different species of aliens?" He asked, trying to wrap his head around the concept.
"Yeah, each transformation is sampled from a representative of a given species. Each with its own homeworld, language, culture…religion." Percy noticed that he hesitated on that last part.
Percy could see why. After all, who's to say only human gods exist, there could be entire pantheons of alien gods out there in the universe. The very thought chilled him to the bone. One pantheon's problems were bad enough, an entire universe worth of gods was downright terrifying.
"Okay Jackson!" He thought. "Pull yourself together. Think of good things: like blue cookies, building sand castles with Tyson, the way Annabeth's hair glows in the sun…"
"Uh dude…" Ben waved a hand in front of Percy's face, snapping him out of his ADHD fuelled rabbit hole.
"Oh uh…what?" He asked.
"You kind of zoned out on me, anyway I found the alien I was looking for!"
"You did?"
"Yeah! It's Hero Time!" He said as he slammed his hand into the dial, triggering a green flash.
A moment later, Percy uncovered his eyes and beheld but looked like a gray ghost, covered in black lines, and possessing a single green eye with the same hourglass symbol that was on the Omnitrix now on his chest.
"GHOSTFREAK!" The creature rasped.
"Why do you shout out names like that? Percy asked.
"It strikes fear into the hearts of my enemies!" The ghost answered.
"Uh huh." Percy replied, rolling his eyes. "So how is this guy gonna get us outta here."
"Grab my hand, Ocean Man!" 'Ghostfreak' ordered.
Percy did so and felt a weird sensation as Ghostfreak went slightly transparent and passed through the wall of the makeshift jail cell, pulling Percy along the way.
Once they made it through the wall and into the hallway, Ben transformed back into human and turned to face Percy.
"Okay here's the plan, while I destroy Animo's mutant ray and generally just do awesome alien things, you distract him with that fancy sword of yours!"
Percy shook his head, "Riptide won't work on him, he's mortal and celestial bronze doesn't work on mortals." A thought occurred to him. "Then again, we're on a ship, which by definition is surrounded by water, the very thing my demigod powers work on… So, I should be able to work with that."
"Great! You do your hydro-voodoo and I'll take care of the rest!"
"Can we not call it my 'hydro-voodoo'?"
"NO! Anyway it's HERO TIME!" Ben shouted as he slammed the Omnitrix again. Transforming into a velociraptor looking creature with blue skin and a black helmet over his head.
"XLR8!" he exclaimed as he ran down the hallway.
Percy just rolled his eyes while thinking: "He talks like a saturday morning cartoon character!" but regardless ran right after Ben.
As Percy ran, he called on the water not only in the surrounding plumbing but also on the outside of the ship, feeling the familiar tug in his stomach as he did so. Soon, pipes were rupturing all over the place creating a tidal wave that carried him directly into Animo's lab."
As soon as he entered, the wave swept through the lower levels of the lab, damaging what must have been thousands of dollars worth of equipment. Eventually XLR8 emerged from the deluge and grabbed onto one of the upper railings before commenting in shock:
"Woah, where was that earlier, Ocean Man!"
"Now that I understand the stakes, it's easier for me to let loose… and stop calling me Ocean Man!"
"Stop calling me 'Creature Feature'!" XLR8 retorted.
"Never!"
"YOU FOOLS!" came a familiar voice from the upper levels of the lab. "You have only wrecked what amounts to my vestibule!" proclaimed Dr. Animo.
"Of course it wasn't that easy!" Both Ben and Percy deadpanned at the same time.
"My true equipment lies on the upper deck, all you have done is make it possible for my mutated creations to reach you better!" He monologued as several mutated sharks swam into the now flooded lab.
Percy responded by summoning a wave to push them back, however he could only keep taxing his powers so far before he tired himself out too much to fight.
"Hey Tennyson, I hope you have an alien that can fight these things, because I'm starting to get tired!"
Ben, still in XLR8 form, responded: "Don't worry, I got this in the bag!" as he tapped the hourglass symbol on his chest and promptly transformed into a humanoid anglerfish and shouted:
"RIPJAWS!"
He then jumped directly into the flood and began fighting the mutated sharks by biting them.
While this was going on, Percy realized: "Well so much for the original plan!" and ran up the stairs to deal with Animo and his monster ray all by himself.
Once on the ship's quarterdeck, Animo beheld the demigod with a smirk. Behind him was the rebuilt transmodulator as well as a hastily built transceiver hooked up to a laptop.
"I was expecting Tennyson, but you are interesting in your own right."
"I aim to please!" Percy snarked.
Animo continued: "While Tennyson's abilities come from that watch of his, yours are more innate, while you were imprisoned I took the time to study your unique genetic code and while I have not fully cracked it yet, I discovered something fascinating…"
"Yeah what?" Percy asked.
Animo hissed: "There are more of you."
A chill went down Percy's spine as he realized the implications of what he just said. "Oh gods if he finds the camp because of me, we're doomed!" he thought. "Play it cool, he might just be saying stuff to get a reaction out of me!"
"What makes you say that?" he eventually responded.
"Once I had isolated the anomalies in your genome, I conducted a scan of the surrounding area and have determined that there are many like you, too many to gain an adequate fix but I know they're out there!"
"I swear if you hurt them…" Percy began.
"And now I have confirmation! But don't worry, I only need one…"
Percy's rage exploded, he launched himself at the mad scientist. So what if his sword didn't work, no one threatens his family like that and gets away with it.
He slammed a fist made out of water into the mad scientist who tanked the hit and stepped out of the way.
"What is this guy made of?!" Percy wondered in exasperation.
Animo held up a remote device and gloated: "I was able to determine that a creature with genetic anomalies similar to yours was nearby and constructed a transceiver to summon it. Which I shall do NOW!" He said as he pressed the button of the remote.
The transceiver sent out a shock wave that threw Percy back as the ship rocked and a whale-like creature emerged with eyes trained on Percy.
"Cetus!" Percy thought. "He summoned Cetus!" Percy recognized the creature from when he and Annabeth would discuss potential monsters they could face. According to legend Cetus had been defeated by the original Perseus, Percy's namesake, using Medusa's head.
"Which I don't currently have!" He thought glumly.
"Tremble before my might…uh…now that I think of it I don't even know your name!" Animo realized.
Percy rolled his eyes. "Might as well!" he muttered. "The name's Percy Jackson!" He shouted.
"Excellent! Now perish by my hand Percy Jackson!" The mad doctor declared.
Suddenly a green flash erupted below deck as Ben Tennyson, now in human form, emerged panting: "It took a while but I was able to get those mutated sharks under control, how have you been holding… OH MY GOD WHAT IS THAT?!" He shouted as he noticed the whale-like Cetus's head hovering over the ship waiting for Animo's command.
"YOUR DOOM! MWAHAHAHAHA!" Animo declared.
Percy immediately uncapped Riptide and slashed at one of Cetus' many tendrils.
"Finally, something that Riptide works on!" Percy thought, relieved to finally have a chance to use his sword skills.
While Percy was doing that, Ben slammed the Omnitrix and became a large blue moth-like creature.
"BIG CHILL" he rasped.
Big chill then unfolded his wings and immediately flew towards the sea monster, going intangible each time it tried to grab him while also freezing parts of its body.
Cetus roared in pain due to the frost-bite, but regardless was able to burst open the ice encrusting his body and continue clawing at the ship.
As the ship lurched and began to capsize, Animo's eyes widened as he realized:
"Oh I just made a catastrophic mistake!"
"You think!" The two teens shouted at him.
As Animo fled to the lifeboat, Big chill turned to Percy and said:
"I have a feeling this has something to do with your world!"
"It does!" Percy confirmed, dodging tendrils. "This thing is called Cetus, it was created by my father to terrorize a kingdom he felt had insulted him, it was killed using Medusa's head the first time!"
"What do you mean the first time!?" Big chill's voice carried over the sound of crashing waves.
"Monsters aren't like us, they can be killed, but eventually they regenerate and come back to hunt demigods."
"How often does this happen?" Ben asked, concerned.
"All the time!"
"How do you live like this?"
"Well, it ain't easy!"
At that moment, Ben let it fully sink in that there were kids his age out there who had to fight Monsters like this all the time and most people didn't know about it except themselves.
"At least I have the benefit of being famous among other species in the universe, these people aren't even acknowledged on their own planet!" The Omnitrix wielder thought.
Suddenly he had an idea: "If this monster can't be stopped on the outside…"
He flew into its mouth, while slapping the Omnitrix dial on his chest. Percy was shocked.
"What are you doing you maniac!? You're not supposed to go in its mouth! The whole point of fighting the darn thing is so that you don't HAVE to go in its mouth!"
But while Percy was ranting at no one in particular, Cetus felt a great pain in its chest, as if it were being burned on the inside.
In its panic the monster slammed down on what was left of the ship, breaking it entirely and sending Percy straight into the sea. The transmodulator, which by this point had been short circuited by the flood earlier, exploded, turning all the remaining mutations into regular sea life again.
Now in his native element, Percy dove towards the sea floor where Cetus continued to thrash in pain and stabbed him in the chest. Now mortally wounded, Cetus dissolved into dust releasing a tremendous explosion of heat.
The source of the heat happened to be one Ben Tennyson in the form of an alien composed of magma and rock. Said alien then struggled for a moment underwater before passing out and reverting back to human form.
Percy quickly grabbed Ben by the shoulders and pulled him to the surface, where he then called on the sea around him to push the two to land.
Now on land, Ben finally woke up and began coughing up water.
A moment past where neither of them spoke until Percy broke the silence:
"So… what do you call that one?
Ben blinked, before responding: "I call that one Heatblast. Fun fact, when I got the original Omnitrix he was the first alien I turned into."
Percy stared into the sea, realizing he now had a LOT of explaining to do when he next saw his father. He could just imagine the conversation:
"Percy, why is there a crumpled barge at the bottom of my ocean, and where is Cetus?"
"Oh that! It's nothing dad, I just fought a mad scientist obsessed with mutating animal life, who also figured out how to summon monsters. Not only that, but I did so with the help of an alien shape-shifter, yes dad I said alien, who I also have to work with now to prevent stuff like this from happening again! So like I said, it's nothing!"
"Son, has Dionysus been serving wine at camp?"
Percy burst out laughing at the hypothetical conversation his brain just came up with. While Ben looked at him like he just went insane.
"Uh dude, you okay?" He asked, concerned.
"No, I'm fine, just thinking of how I'm gonna spin his situation to Dad. So what now?"
"Now we must formalize our alliance!" Said Hecate who just appeared out of nowhere.
"Gah!" Went Ben, taken by surprise. "I'm never gonna get used to that!"
Percy smirked: "Just like I'm never going to get used to that transforming thing you do."
Hecate ignored this exchange and continued: "In order to ensure that this agreement is iron-clad. Both of you must swear on the River Styx never to reveal the existence of the other's world to anyone you know!"
"Swear on what now?" Ben asked.
"The Styx is the river of oaths in the underworld, an agreement sworn by its name is binding unless it is agreed by all those involved to dissolve it. Be warned, Benjamin Tennyson, to attempt to break such an agreement will bring a fate worse than death."
Ben gulped before replying: "Fine I swear on the River Styx not to reveal the existence of Percy's… unique family to anyone I know."
Hecate nodded: "That is sufficient. Perseus Jackson what of you?"
Percy also swore on the Styx not to reveal Ben or the existence of aliens to his friends.
"Then it is done! One more thing Perseus, in order not to compromise your mission, I persuaded Iris not to let certain messages get through to you."
Now it was Percy's job to gulp. "W-what kind of messages?"
"Messages from a certain girlfriend of yours whose date you have missed. Oh look, there's one now!" She pointed as she disappeared.
Ben immediately stepped out of the way as an Irate voice came from a miniature rainbow that had just appeared on the scene.
"SEAWEED BRAIN! WHERE THE HADES HAVE YOU BEEN?!"
Percy's face paled: "Wise girl, I-"
"Don't you 'Wise girl' me! I've been looking everywhere for you, I thought you had gone missing with amnesia again!"
Ben couldn't help but raise an eyebrow at that from behind the Iris message. Percy gave him a look that said: "Not now!" before continuing to reason with his girlfriend.
"Annabeth, I was attacked by a monster on the way to dinner, and it took a while to… deal with the situation. I'll meet you at camp to explain everything!"
"You better, I almost called in the Hunters to start looking for you like last time!" She said as the IM faded.
"Ooh, you're in trouble!" Ben mocked.
"Shut it creature feature, shouldn't you be dealing with our mutual friend?"
"Sure thing, he'll be in jail before you know it. See ya around… Ocean Man."
As Ben and Percy parted ways, Ben received a transmission on the Omnitrix:
"Ben, where are you? It can't have taken this long to deal with Animo!" Came the voice of Ben's cousin, Gwen."
"I bet he got lost or got his butt kicked!" Said the voice of Kevin Levin.
"Oh ha ha you guys, let's just say there were complications, I'd rather not talk about it. Wanna meet at Mr, Smoothies once I get back to Bellwood?"
THE END
(So what did you think? Keep in mind this is my first fanfic and that I am open to CONSTRUCTIVE Criticism.)