Well, this wasn't what I had planned for my first fic on the site, but dammit, Judge Royce isn't updating and I don't feel like waiting. So, here it is, my own Ben 10/Mass Effect crossover extravaganza.

Okay, quick heads-up: Ben has his Ultimate Alien look with the new white Omnitrix. However, the events of Omniverse have not occurred. Therefore, Rook will not be in this story.

Disclaimer: I own nothing.

Special thanks to Judge Royce, The Incredible Muffin, Bigby the Big Bad Wolf, Codecrash, and Ultimate10 for inspiring this story. They are, without a doubt, my favorite Ben 10 crossover writers on this site.

Chapter 1: The Paradox Effect

It was ironic, really.

When he was fifteen, Ben Tennyson craved an ordinary life, without aliens and criminals and the Omnitrix. He could go to high school, find a girlfriend, play soccer, enjoy smoothies, and hang out with his favorite cousin without the stress that came with the superhero lifestyle.

Now, Ben is eighteen, and he is starting to wonder just what the hell he was thinking. Ever since he and Vilgax had their final showdown two years ago, everything had become too easy. Azmuth had put together a team of the brightest Galvans in the galaxy (which was saying a lot) for the sole purpose of creating better technology for the Plumbers to use, which gave them a huge advantage when it came to handling lawbreakers.

On the plus side, this meant that super criminals such as Animo and Rojo were able to be detained much more effectively than ever before.

On the down side, it meant that the Plumbers were so good at their job that Ben was practically obsolete. Other than the occasional bank robber or hostage-taker, the teen hero had nothing to do.

After graduating high school, he managed to move into his own apartment, making money by selling off shards of crystal and manipulating the stock market (thanks to Diamondhead and Grey Matter, of course). Therefore, he did not require a job.

However, Ben was still unsure about college. On the one hand, he did see the need to further his education, along with the fact that it would make his mom happy. On the other, he was a superhero who could make upwards of $100,000 in less than an hour, so college seemed kind of useless at this point.

Nevertheless, he promised his parents that he would give it some thought over the summer.

At the moment, however, college was the farthest thing from his mind; Ben was currently sitting at Mr. Smoothy's and enjoying his favorite beverage. Unfortunately, he was sitting by himself, as Gwen had long since gone off to an Ivy League college, with Kevin working at a mechanic's near said college in order to stay near Ben's cousin. Other than them, he didn't have many friends, other than perhaps the Plumbers' Helpers.

He also didn't have a girlfriend, he and Julie having broken up long ago. Since then, Ben had been unable to find a girl to fill the void, as most of the ladies interested in him only cared that he was famous, and didn't bother to get to know him as a person first. It made him wish for his secret identity back.

Sighing, Ben finished off his smoothie and tossed it into a trashcan sitting a few feet away.

"Hm. What should I do now?" he asked himself, crossing his arms over his chest. Being famous across the universe made it impossible for the wielder of the Omnitrix to go anywhere without legions of fans swarming him. The only reason he was alone right now was because everyone in Bellwood was used to his presence.

"I bet Rex never gets this bored," the teen groaned, referencing the friend he had made from an alternate dimension where human beings were infected by machines called nanites. That had been a weird adventure.

"And there's my cue!" came a cheerful voice with a British accent. Ben quickly turned around, only to see the familiar labcoat-wearing form of Professor Paradox standing a few feet away.

"Hey, Professor," the eighteen-year-old smiled as he slipped his hands into his pockets. "What universe-saving adventure am I going on this time?"

Indeed, whenever Professor Paradox showed up out of the blue like this, it usually meant that the universe, or the time stream, was in danger. Such a shame, really. The time-walker was a pleasant person to be around, but his appearance almost never boded well

"An excellent question!" the time-traveler exclaimed before holding out a brown paper bag. "Gumball?"

Ben politely declined.

Shrugging, Paradox slipped the bag back into his coat. And with that, his face became grim and stone-like. "Benjamin, I come with grave news."

"I figured."

"Recently, I've been using my abilities to cross the barrier between dimensions, exploring many universes and witnessing quite a few incredible events." The Professor then gave a playful smirk. "In fact, I've come across many that involve you."

Ben cocked his head in confusion. "Really?"

"Oh, yes. Quite a few interesting things have happened to you in these alternate realms. In one, you marry an incredibly powerful woman and have a son with a myriad of special abilities. In another, you have joined a guild of magic users, as well as being the first person to create a smoothie."

The teen grinned, feeling a sense of pride, though his smile disappeared when Paradox resumed his 'impending doom' face.

"However, that is not why I'm here now. You see, Ben, I have come across a particularly fascinating universe, where the Milky Way galaxy possesses only a handful of sentient species that run the galaxy, including humans."

The wielder of the Omnitrix narrowed his eyes in thought. The galaxy was such a vast place; how could only a few different species control it? There should be thousands, if not millions of different races coexisting with one another.

Paradox continued. "Upon further investigation, I discovered that this alternate galaxy was built on a cycle of extinction."

"Wait, what?" Ben asked, his blood running cold at the word 'extinction'.

"You see, every fifty thousand years, different races evolve to the point where they can take to the stars and colonize other planets, like in most science fiction. But at some point, large mechanical beings known as Reapers appear and cleanse the galaxy of all sentient life, erasing their history, culture, technology, everything. Then they come back fifty millennia later and do it all over again."

Ben felt a powerful urge to vomit, along with an overwhelming desire to take these 'Reapers' down.

"Now, the cycle is about to begin again, and the Reapers are currently scheming from outside the Milky Way," Paradox explained. "It is my hope that you can end this cycle once and for all."

The teen didn't hesitate. "When do I start?"

The Professor smiled. "Good show, Ben. Now, you're a quick study, so you'll be able to figure out more about this universe once you're there and have access to their records. But I must explain a few things before I send you on your way."

"Like what?"

"Well, first off, your mission: the Reapers are using beings known as Collectors to abduct human colonies. They look like humanoid insects, but don't let that fool you. They are nothing more than shells, made up of technology and dead flesh."

"So what, they're robot zombie bug people?" Ben asked.

"In layman's terms, yes. The reason I'm telling you this, Ben, is because you must not hesitate in putting them down for good."

The teen's green eyes widened at Paradox's supposed ruthlessness.

Sensing the eighteen-year-old boy's distress, the time-walker gave a sad smile. "Trust me, you will be doing them a kindness. They are slaves to the Reapers, nothing more than cannon fodder." After a brief silence, Paradox continued the briefing. "Now, this is a large task I'm assigning you, so don't expect to go it alone. A human by the name of Commander Shepard has managed to hold the Reapers at bay two years ago, and is now putting a team together to take the fight to the Collectors and stop the abductions."

Ben nodded in understanding.

"You have to realize, Ben, that the people on this team are not as virtuous as you. Every single one of them has killed before, and will kill again. Some of them are ruthless, others are noble, but in the end, none of them will hesitate to take a life if they have to."

"Why are you telling me this?" the boy questioned suspiciously. He was not a killer, and he never would be.

"I'm not asking you to shed blood, Ben. Just for you to keep an open mind and not judge these people too harshly. Many difficult choices lie ahead of you, some of which may indirectly cause multiple deaths. But you must not falter in your conviction," Paradox said, looking troubled. He reached up and pinched the bridge of his nose.

"I have seen the atrocities the Reapers commit. They slaughter everyone equally, man, woman, and child. If they don't kill you, they shatter your mind and turn you into a slave that can no longer think for yourself. They convert living beings into bio-mechanical monsters that remorselessly murder the people they used to love, and in the end, when the last hint of resistance is crushed..."

Ben felt his gut twist as he saw tears form in Paradox's eyes, which the Professor quickly wiped away. "I know you, Ben. You will do everything you can to fight this threat, and even make a few new friends along the way."

The eighteen-year-old savior of the universe stood tall. "I'm guessing you already told Grandpa about this?" he asked, knowing that his grandfather would tell Gwen, Kevin, and his folks about the mission at hand.

"Correct."

The teen cracked his knuckles. "Well then, what are we waiting for?"

Paradox smiled with a hint of pride. "I'm sending you there now, then. You will arrive on a planet known as Horizon, a human colony that is currently being attacked by the Collectors. While I urge you to save as many people as you can, you must meet up with Commander Shepard and convince him to allow you on his team."

The British man then pulled out his pocket watch. "Oh, and do be patient with Miss Lawson, will you? I daresay it will be worth it in the future," he smirked.

Ben was about to ask who he was talking about before being engulfed in a bright flash of light.

A few blinks and a shaking of his head later, Ben saw that he was standing somewhere very different than the parking lot of Mr. Smoothy's. He was currently in some kind of clearing, surrounded by strange white buildings. Littered around the clearing were what looked like crates, and a circular platform with a large antenna on it. All around the area, strange bugs were buzzing through the air, though they paid him no mind. Turning around, he felt his jaw drop when he saw a massive ship that might even give Way Big a run for his money.

A sound from his left caused Ben to look over and see a group of strange creatures with brown chitin-like skin, four pale-yellow eyes, and, to the boys chagrin, organic-looking guns that were currently being pointed at him.

"Oh, man!" the teen grumbled as he dived behind a nearby crate, narrowly avoiding a yellow blast of energy that had been aiming for his head.

Ben quickly activated the Omnitrix, looking for an alien that would be able to take down these enemies (which he presumed were the Collectors, as they looked like humanoid insects) while also providing decent defensive capabilities against their energy weapons.

"Gotcha," he smirked as he slammed down on the dial.

A bright flash of green light later, and the eighteen-year-old human was replaced by a seven-foot-tall being with a dark indigo body that appeared to be made of rock, crystal-like arms that looked like they could do some damage, along with two matching spikes jutting from its back.

"DIAMONDHEAD!" the alien bellowed as he stood up, sharpened his arms into blades, and charged his bug-like foes, who continued to fire their beam weapons. The blasts stung slightly, but did no damage to the transformed teenager.

Feeling slightly sick at what he was about to do, but trusting Paradox's judgment, Diamondhead lunged forward and shot his right arm forward, impaling the Collector at the front of the group through the stomach.

The Petrosapien winced, though his disgust was offset by the fact that his foe simply looked right at him and began lifting its rifle up in order to shoot him in the head, completely emotionless in its movements.

Looks like the Professor was right, Ben thought as he withdrew his arm and took a swipe with it, taking the alien's head clean off. Before the body collapsed to the ground, Diamondhead managed to see a glint of some kind of metal in the neck of the now-dead Collector.

Feeling a little relieved that he wasn't necessarily killing real beings, the teen hero quickly went to work, slicing open two more of the bug aliens with one swing while punching a hole through the chest of another.

After a handful of seconds, all but one of the Collectors were dead, and Diamondhead gave the lone survivor a glare.

"I'm guessing you don't talk, do you?"

Instead of a response, the human-abducting alien dropped its gun and began convulsing, with cracks of glowing energy appearing in its armor. The Collector then floated into the air and unleashed a surge of power that knocked Ben back a step.

"I'll take that as a 'no'," Diamondhead muttered as he assumed a defensive stance.

The Collector landed on its feet, glowing with a fiery aura, its eyes glowing like miniature suns.

"WE ARE HARBINGER."

"Good for you," the transformed teen retorted as he fired three diamond shards at the upgraded Collector, two striking its chest and one in the shoulder. The glowing alien didn't even flinch.

In retaliation, the Collector extended its arm and fired a sphere of glowing energy at Diamondhead, who lifted his arms into the air, using his powers to summon a large crystal prism to rise from the ground and block the attack. The sphere struck the prism and exploded violently, shattering the diamond wall.

Ben blinked in surprise. "Well, that's not good."

"YOUR SPECIES IS UNKNOWN. YOU WILL BE STUDIED."

Instead of responding, Diamondhead transformed both of his arms into blades once more and charged forward, intending to bifurcate his opponent. Just as he was in striking distance, however, the Collector released a pulse of energy, shattering the diamonds on his back and sending him flying backwards.

Ben landed with a grunt, his body aching from the blast. It felt like he had just been hit by Vilgax.

"Okay, close range is a no-no," he noted to himself as he reached up and tapped the Omnitrix symbol.

"FEEDBACK!" cried the new alien that emerged from the green light, which had a singular green eye, a white stripe running down its body, two antenna, and a tail.

"SHAPESHIFTING CAPABILITIES. YOU ARE AN UNKNOWN. YOU WILL BE ELIMINATED."

"Yeah, haven't heard that one before," Feedback grinned as he picked up a nearby crate and chucked it at the Collector, who swatted it aside effortlessly. Once more, it launched an energy attack, which Ben had expected when he picked his Conductoid form.

Outstretching his hands, Feedback allowed the attack to make contact with his fingers. Almost instantly, the orb shrank in size and disappeared, having been absorbed by the transformed teenager.

"Sorry, that was rude to steal your energy without permission," Feedback joked as he lowered his arms. "Here, you can have it back!"

With that, he pointed his antennae at the Collector and unleashed a massive blast of blue power, which engulfed the bug alien in its bright light.

When the attack was finished, there was nothing left but a smoking crater in the ground where the upgraded Collector once stood.

"Guess he could give it, but he couldn't take it," Ben quipped as he looked around. "Now, where exactly do I-"

Feedback's talking to himself was interrupted when he was suddenly hit from behind by a strong force, sending him flying forward and landing on his face.

"Is this gonna be a thing now?" he muttered to himself in annoyance, his voice muffled by the dirt his face was planted in. With a groan, he used his hands to push himself back onto his feet. Turning around, he saw quite a strange sight in front of him.

Seven people, both human and alien, stood a few meters away, with their weapons drawn and pointed straight at him.

Up front was a tough-looking man wearing grey armor that had a red stripe running down his right arm. Ben assumed that he was the leader, given the fact that he was at the front of the group.

Next to him was a bird-looking alien wearing blue armor and some kind of visor over its left eye, while the right side of its face looked heavily scarred.

On the other side of the leader was a muscular dark-skinned man wearing a black outfit, whose eyes were wandering over the area in an attempt to locate any more hostiles.

At the back of the group was a large dinosaur-like alien wearing silver armor with some kind of ridge on its head. It glared at Feedback with bloodlust in its light blue eyes.

Another alien, this one looking somewhat lizard-like and wearing what appeared to be a strange lab coat was fiddling around with a holographic device on his left arm.

It took all of Ben's willpower not to stare at probably the most beautiful woman he had ever seen, with magnificent curves enclosed in a skintight catsuit that left little to the imagination.

Unfortunately, his attention was focused on what appeared to be a bald woman wearing baggy pants and a belt that barely covered her chest, who was glowing with blue energy not dissimilar to what the Collector was doing earlier. Her lips were pulled back in a snarl, as if she were waiting to tear Feedback apart. Ben was willing to bet that she was the one who hit him from behind.

"What the hell is that thing, Commander?" the dark-skinned man asked. Wait, 'Commander'? As in Shepard?

"I don't know," the leader admitted, staring at Feedback with a critical eye. "But the seeker swarms haven't paralyzed it, so I'm guessing it works for the Collectors."

Uh-oh.

"Good, then I can tear that fucker's tail off and choke him with it," the bald woman snarled as her blue energy glowed brighter.

"Perhaps take in alive?" the lizard alien asked. "Could dissect, run tests, learn more about Collector technology."

"We could send samples back to the Illusive Man," the beautiful raven-haired woman suggested.

The leader frowned at that sentence, as if he found this 'Illusive Man' repulsive. "No time. If we want to save the colony, we gotta take this thing down hard and fast."

As Ben was getting ready to protest, he felt something sharp against his throat. Blinking in surprise, his eye widened when a figure seemed to shimmer into existence in front of him. It was a woman, wearing a black outfit and hood that concealed everything except her twinkling eyes and mischievous grin. She seemed unfazed as she held a knife to his throat.

"Hi there," she said in a playful voice. "Wanna give up now?"

Feedback let out a sigh. "Aw, man."

I know this chapter is kinda short, but I wanted to save the fun stuff for next chapter, where Ben may or may not have to fight Shepard's crew (spoilers, after all). Then they'll have to team up against the Collectors and that damn Praetorian.

Okay, a few notes before this story goes on: First, yes, I chose a Male Shepard. Why? Because if I did a FemShep, I'd have no choice but to have Ben romance her. Yes, I love Jennifer Hale that much.

Second, Shepard is a multi-class. Why? Because I said so. He won't be OP, but he'll be deadly as hell.

Also, here's the pairings for the fic. Don't like, that's your problem.

Ben/Miranda
Shepard/Liara
Joker/EDI
James/Jack
Garrus/Tali

Why am I telling you this? So there's no confusion or doubt. I'm locked in my current course. And if you're wondering where Zaeed is, don't worry. I have a plan for him.

Fifty internet points to whoever can spot the references to two of my favorite fanfics.

So yeah, reviews will be put in syringes and injected into my arm. (This is a joke, DON'T DO DRUGS, KIDS!)

Flames will be used to burn copies of "50 Shades of Grey".

Big thanks to The Incredible Muffin for helping me out and giving a few pointers. Seriously, read his stuff, he hasn't had a single bad story yet!