Rex.

"You're sure this will work?" Rex crossed his arms and looked over at his brother, bent over a work table with a small welders torch.

"98.6% sure," Caesars muffled voice responded from behind the welding mask. "If my calculations are correct, then modifying the dimensional disruptor to target-"

"You mean the 'null void gun'," Rex chimed, "thats what alien kid called it."

"Not exactly. This was the null void gun I used to get rid of the Alpha Nanite, but hopefully with the changes I've made, the portal it creates will open up directly into Ben's dimension."

"How does it work?" Asked Six.

"The null void dimension links this dimension to Ben's, so theoretically we can use that connection to travel to his universe. If I could just..."

"I don't know about this Rex," Doc, who had been looking over Caesars notes, spoke up. "I mean.. Dimensional travel? We don't even know if this will work."

"He's followed the pack into Ben's dimension before." Six said pushing his shades farther up his nose.

"I didn't like it that time either," Doc muttered.

"I'll be fine Doc. Besides, Caesar upgraded the communication system so you can talk my ear off the whole time I'm gone." Rex smiled and tapped his earpiece.

"The coms. upgrade is untested. So is the dimensional projector. And if Van Kleiss really is hiding in that dimension like we think he is, there's no telling what he's capable of after all these months. I just think this is a bad idea."

Rex's smile faded and he turned his face away. "Doc. You know why I have to go." Holiday looked up at him sympathetically about to respond-

"There!" Caesar exclaimed lifting his mask away and holding up the projector. "Now all that's left is to see if it works. Are you Ready Rex?"

"I'm ready." Rex said shifting his goggles down over his eyes. Caesar moved to the open part of the lab and started up the gun. Caesar braced as a golden glow started from the front until it burst forward in an arch of light, congregating into a ball of energy that grew into a swirling portal a few feet away. The lights flickered for a moment.

"I could still come with you," Six said placing a hand on Rex's shoulder.

"Would you guys quit worrying? Like you said, I've done this before, I know my way around. You'd just slow me down" Rex resuming his usual playful smirk. Six nodded taking a step back.

"Fine. But don't forget my samples." Doc fastened a pouch around Rex's waist.

"Again with the samples Doc?" Rex turned towards the portal.

"Be smart, kid," Said Six. Rex gave him a nod and disappeared into the golden glow. "I hope he finds her."

End of Prologue.

Authors Note:

Here's a little context: This crossover extends the canon timeline of each show to the fullest extent possible. This means that whatever character you see within this fanfic will have experienced everything the actual authors of the show wrote. For Rex this means that this takes place a few months after the series finale of Generator Rex. For Ben this story picks up right after the end of Omniverse. We see Zak in Omniverse, in the episode TGIS, and it's three years after the events in The Secret Saturdays series finale. This also means that Ben has been to Rex's universe in the crossover special Heroes Unites, and Rex has been to Ben's universe in the comic Heroes Times two. So Ben knows both Rex and Zak from previous encounters, Zak knows Rook, Rex knows Gwen and Kevin, etc. Hope you enjoy!