The Legend of Ben 10: Book 1, Sentience.

Chapter 4: The Chase

"Where exactly are we going?" Ben asked as Azula led him further and further down a large flight of stairs. 

"Like I said." said Azula. "To meet the others.."

Azula opened a door at the bottom of the stairs that was glowing orange in the torchlight. The door creaked open to reveal a large red colored arena surrounded  by large hanging banners that were emblazoned with the moon crescent  

Two people were fighting in the center of the room. 

The both of them didn't look much older than Ben.  One of them was a girl with bobbed black hair, her features European, something that Ben immediately noticed in a mostly Asian world. 

She wore Fire-nation style armor similar to Azula's own black armor over read clothing, and she was punching her fists through multiple blobs of what appeared to be green energy in liquid bubble form. 

The glowing green jelly-like bubbles that had glowing energy spheres in their centers were being generated by the hands of a boy who also looked European. He had similar armor, with sandy colored hair and green eyes. 

"Ha! On the ropes now!" The boy exclaimed, grinning. 

"Oh screw you." the girl muttered. 

At that moment Ben realized that she wasn't punching through the energy spheres as the ones that missed her bounced several times like rubber balls before exploding into massive plasma bolts, but the ones that touched her fists disappeared.

Rather she was absorbing them. 

Ben's initial suspicions were confirmed as the girl smacked her hand to the floor and stone armor coated her body. 

"An Osmosian." Ben muttered without thinking.

The boy and girl stopped fighting as the girl grinned, putting a hand on her hip and looking up at Ben. "Hey hey! Somebody knows his aliens. Actually I'm half human. How'd you know?"

"Because Ben Tennyson here is like you." said Azula, causing Ben's spine to freeze from end to end. "He's from your era. "

The girl stared with awe as the boy looked shocked. 

"N-No way, y-you're Ben 10!?" the girl squealed. 

"Y-you." Ben turned to look at Azula. 

"Oh please.. Bob Fire? How dumb do you think I am? And honestly that fool Sokka. I know you're here with the Avatar's friends." said Azula. 

"DAMNIT SOKKA!" Ben wheezed. "Then why!? Why haven't you-?"

"Killed you? Tennyson, you're a valuable asset whose on the wrong side of this war. I don't know what they've told you about me, but the Ladies stand against the Avatar because the Avatar stands against the natural order and righteousness of this world. They're the good guys! Something I'm hoping you'll understand as Earth's former defender yourself." said Azula.  "These two have told me a lot about you."

"Mia!" the Osmosian girl clasped her hands over Ben's hand and shook it, looking nervous and excited. "U-uh, I'm your biggest fan! I've been to all your guest appearances 10 million years ago!"

"The name's Chris, don't expect me to go hug you or anything, but I'm a fan too, I guess." said the boy with a wave. 

"Th-they're-."

"Mia's the only extraterrestrial connection here." said Azula. "Chris is a mutant who gained strange abilities after he woke up from his cryo sleep. You're not the only one who was sleeping Ben. There are others, others out there still from your time."