RWBY x Ben 10 crossover

The Boss of the Grimm

Once upon a time, there was two gods who watched over Remnant...back when the moon was full...in this land of peace man and Faunus lived in harmony alongside the rest of nature. The two gods both represented a side to humanity as we know it today, the light god gave us our ability to think and create whilst the dark god gave us our ability to destroy and cause harm. We were the creation of both gods working together however the dark god had another creation, one with the soul purpose to destroy...the creature of Grimm. They were fully under the control of the Dark God and only lived in the dark kingdom their creator lived in. After a tragic accident a woman tried exploiting the gods to get her fallen lover back, this woman's name was Salem. After the god of Light refused to help her, Salem attempted to seek assistance from the god of Darkness who she lied to saying she went to him first, however the god refused to bring her lover back after her lies crumbled. Due to neither of the gods helping her, Salem saw the gods as nothing but evil so she led a rebellion with the rest of mankind against the gods, forcing them to retreat from our world and the moon shattered in the process. After many years she learned how to control the Grimm, who were left behind by the gods, with the sole intention of destroying humanity.

"Over the years, Salem has been forgotten to the public...however there is a select few who remember Salem and are actively searching for a way to put her down." Ozpin explained as I felt I could finally put together the dots.
"That's why huntsman academies exist, to raise warriors to put a stop to Grimm." I finished his sentence as he nodded.
"Yes, the public cannot learn about this Ben. It'll cause widespread panic and only give Salem the chance to wipe out humanity." Glynda spoke.
"Don't worry I won't say anything, we have to stop her after all." I said as Ozpin shook his head.
"No, we have to stop her...you need to get home."
"I refuse to leave all my friends in danger because of Salem, I won't go back until she is put down." I replied as a small smile formed on Ozpins face.
"I see, well then welcome to the resistance Ben." Professor Ozpin welcomed me as a cold hand put itself on my shoulder.
"We're happy to have you help our battle." Ironwood spoke as I got up from my seat.
"I should probably go let Azmuth know I'm not heading back home any time soon then, shouldn't I?" I joked as Ozpin nodded.
"Azmuth?" Ironwood asked.
"Someone else from my universe who is trying to find a way for us to go home." I explained, forgetting to mention the fact Azmuth is an alien.
"I'll join you Mr. Tennyson, lest you endure Azmuth's wrath alone." Glynda said as she followed me to the elevator before Ozpin spoke up.
"And Glynda, as a warning I've heard the other member of the inner circle is on their way here." Ozpin spoke up as Glynda froze and let out a sigh of pain.
"Of course that drunkard shall be joining us." She sighed as we entered the elevator and went down to the tenth floor of Beacon Tower.

As we entered 'my' office, we saw Azmuth tinkering away with a device that was scanning the two keys of the Ultimatrix that we have found so far, the device connected to a monitor which showed two pings in the centre of the screen and one in the south-east. Approaching him he connected a couple wires as a string of text appeared on the monitor "I knew it, that lock is for a Celestialsapien transformation." Azmuth said smugly as he grabbed the two keys and locked them in a secure drawer before turning to us.
"Hey Azmuth, find the last key?" I asked as Azmuth nodded.
"The last key is in the South West of Vale, though the Grimm activity is high. We might be best off sending Kevin in to scout the place out." Azmuth said as I sighed.
"I hate having to send Kevin into all the missions to retrieve the keys, I wanna go kick some Grimm butts!" I complained as Glynda spoke up.
"We need you here Ben, in case of another attack on Vale." Glynda explained as I groaned.
"I know, I just feel useless right now...apart from training up Alan I have had no action in the past week or two." I sighed before looking at Azmuth.
"That look in your eyes Ben Tennyson, you want to stay in this world when I have made the portal home...right?" Azmuth asked as my eyes widened.
"How did you know?" I asked in shock.
"I'm the smartest being in over 5 galaxies, I know when someone doesn't want to leave their life behind...but have you fully thought this through?" Azmuth asked as I shook my head.
"No, I haven't...but I know deep down this is the right thing to do...I understand if you have to take the Ultimatrix back to our universe with you." I softly said as Azmuth shook his head.
"No, it's yours now...Besides I never wanted the Ultimatrix to exist in the first place." Azmuth brushed it off as he went back to working on his device.
"Thanks Azmuth, so is there anything I can do to help you get back home?" I asked.
"Please transform into Gray Matter, our combined intellects will make this easier." Azmuth requested as I nodded, activating the Ultimatrix before slamming my hand down.

Suddenly I felt my body elongate, my legs turned into skinny pricks as another set of legs appeared out of my body and my head started getting bigger and I could feel the control of my skull of all things come to me.

As the green light faded there I stood, a crab like alien with a massive head. "Hmm, this form is truly interesting. It seems my Intellect has increased," I said as I backed up slightly and opened my cranium up to reveal my brain which let out a few sparks (and also made Glynda flinch at the sight) "Electrokenesis powers too? Then I find it appropriate to name this transformation Brainstorm!" I called out triumphantly as I rolled the R in the name I had dubbed for myself.
"Oh great, don't let your knowledge get to your head now you're a Cerebrocrustacean." Azmuth sighed, the long feud between his species and the Cerebrocrustacean's making Azmuth not want to deal with me in this form.
"Oh please, I would assume this form would be much better suited to apply corrections on the machine you haven't got functioning yet." I taunted as I noticed Azmuth glare at me.
"Why did I have to get every species in the Omnitrix?" He asked himself as he pointed me to another part of the machine, which I started working on with haste as Glynda looked at me with disgust.
"I...I don't like this transformation." Glynda sighed as she looked at my exposed cranium as I worked.
"Feel free to assist Azmuth, instead of looking at me- he clearly needs the help." I bragged as Azmuth glared at me.
"Oh please, your big meaty claws will just get in the way of the finer details that need to be configured." Azmuth retorted.
"These 'big meaty claws' are more then capable, besides I believe the old saying goes 'There is multiple ways to skin a cat.', something you seem to only have one solution for." I taunted as electricity sprouted from my large head as the pure electricity made the wires float and start combining.
"Show off." Azmuth growled as I let out a chuckle, letting him know I considered this mental back and forth my triumphant victory.