AN: After browsing through the crossover archive recently, I noticed that an actual crossover with Ben 10 and Fullmetal Alchemist hasn't been done yet considering that pretty much every other anime has been done already. So it pleases me to be the first author to do so. Omniverse never happened in this story but that doesn't mean I won't borrow any elements of that series. I decided that the only way I could make this work is by bringing in Eon and some of Ben's most dangerous foes into the mix as Ben 10 villains don't exactly get featured very much in these kinds of stories and that Ben could probably take on the Homunculi by himself. Really, that's all I have to say about this one, I'm really excited to see where it goes and hopefully, you guys can enjoy it too.

Liore

Dusk was settling in the town of Liore, as the riots between the loyalists and the so called heretics raged on. However, up in the belltowers of the Cathedral, something sinister was taking place. the Homunculi had been watching from one of the windows, looking down at the people below.

Humans were truly a despicable species.

A cacophony of battle cries and screams echoed throughout the town of Liore. The metallic scent of lifeblood permeated the atmosphere, mixing with smoke and ash as a result of tragic deaths. Ah, she could feel all the suffering in the air, and the anticipation of what was to come.

"Look at them all, humans are foolish beyond salvation," Lust remarked.

Generally useless too, for Cornello's incompetence and failure had forced her to take matters into her hands. Drunk with power of the Philosopher's Stone, he disobeyed her words, and turned into a flailing mess of a monkey.

Though, she was irritated by Fullmetal and his brother's interference. They were meddling little pests who kept getting in their way, and she couldn't even kill them for that as they were important human sacrifices. At least, they gave her a valid reason to get rid of Cornello once and for all.

"Foolish, foolish!" Lust patted Gluttony's head as he echoed her thoughts, watching the spectacle of the human conflict together from the church's tower. It was like a war between two factions of ants, one devoted followers of the fake god Leto and the other heathens who defied said god. She hummed in appreciation when more blood was spilled to the ground, feeling remorseless over the deaths of insects beneath them.

"Fools indeed. Sad, but true." 'Cornello' said as he walked up the stairs of the tower.

"Well, well, if it isn't the Father." Lust said.

"Father." Gluttony said.

"Sorry to have to put you to all this trouble." Lust said.

"As soon as we have everything handled over here, I have my own responsibilities I have to get back to." Envy told them.

Lust smirked and turned her head to the side. "The Fullmetal boy's interference was irritating, but at least we were able to make it work in our favor. Looks like we'll finish up ahead of schedule."

The land was overlooked with the sun starting to sink. "Manipulate a little information and I whipped up the believers, and that's all it took to get this. Humans are such simpletons."

"Bloodshed gives way to more bloodshed, hatred breeds more hatred, until all the violence soaks into the land." Lust's tattoo was shown. "Craving rivers of blood." Her face was shown as she continued. "And no matter how many times it happens, they never learn. The human race is made up of violent, miserable fools."

"Who seem more than willing to play into our hands." 'Cornello' said, causing Lust to smirk.

"Are lots of people gonna to die again?" Gluttony asked.

"Yes, they will." Lust said.

"Can I eat all of them after they die?" Gluttony asked.

Lust petted Gluttony's head. "No, you can't." 'Cornello' was shown, smirking. "By the way, Envy, how long are you planning to look like that? It's very unattractive."

The priest grinned, before red lightning bolts appeared out of his body.

"Hey, hey, I was just going with the flow," he said as his body rapidly transformed, his voice became a dissonance of a gruff and a mischievous young voices. "But I guess it's better to transform into someone young and cute, huh?"

A teenage boy was revealed, with long spikes of black hair and attire that were familiar to her. He grinned when one of Cornello's followers gasped in disbelief.

"M-m-monster!" The follower screamed. "W-what's this?! Where's the real Father Cornello?!"

"What should we say?" Lust asked.

Envy sighed, "He called me a monster. That was rude, huh?"

Gluttony appeared behind Envy, staring at the follower. "Can I eat him?"

Envy and Lust looked at him before the sounds of eating took place of the scene. While Gluttony ate him, Envy leaned against the railing of the balcony.

"Oh, hey, did you hear the news? Shou Tucker, that alchemist in East City, he's dead." Envy said.

"Tucker? Why should we care about a little nothing like him?" Lust asked.

"Because it was him responsible for the murder." Envy said, "Hey Gluttony, you mind chewing with your mouth closed?" He grumbled as Gluttony looked up with a mouthful of flesh from the unfortunate priest who stumbled upon them.

"Don't bother, I doubt this pathetic creature knows anything about table manners," A voice answered from the darkness, causing Lust and Envy to spin around, ready for a fight. Instead, they were met with a pair of glowing purple eyes illuminating in the dark. "Who the hell are you?" Envy demanded, the figure then approached the light. Revealing a man with a muscular build. He wore a silver helmet with a purple visor that blocked all view of his face, leaving only two glowing purple eyes visible. He wore a black bodysuit, and had silver boots, gauntlets, and a chest plate, a purple cape was also hanging off his shoulders. The duo's eyes widened. "What?!" Envy demanded, voice seething with rage and frustration, "Where did you come from?!"

"Where, you may ask?" The armored man repeated in bemusement, "Somewhere your feeble mind couldn't hope to comprehend," Both homunculi turned to see that the surrounding area was actually aging into dust in this being's presence much to the homunculi's shock and disbelief. "I've been wanting to visit this world for quite some time," the figure spoke in a condescending tone, "Do not worry. I'm not here to hurt you...for now."

Envy growled at him and was ready to respond with a biting remark, but Lust stopped him, giving him a look of warning. "Who are you?" she demanded, "What is it that you want?"

"I suppose introductions are in order," the figure responded, "You may call me Eon, Master of Time, and me and associates would like to discuss some business with the one you call...Father or should I say Dwarf in the Flask?" The two homunculi looked at each other for a moment as if considering their options silently. Finally, they nodded and decided to listen. It was probably good for their health if they didn't decide to test this stranger's patience...

AN: Hope you enjoyed the prologue as the next chapter will deal with Ben's arrival in the FMA universe.