What you recognize I don't own and you REALLY need to watch Kamen Rider x Super Sentai Super Hero Taisen to fully understand the story because this revolves around the whole thing, it will begin shortly before the start of the movie and end shortly before the big plot twist where it's revealed that everything that happened in the movie was according to a plan by two of the main characters in their respective franchises and this is entirely in English by the way and I will mainly be using either Rider names or in the case of Sentai the name they are most commonly known as throughout the series, and yes there will be skipping around a little bit seeing as how the movie has the main plot, I'm just inserting what I imagine would happen during some blank periods throughout the movie so as to give a better understanding of what was going on in the background behind their actions

Marvelous was not happy about rumors he was hearing recently about the return of Zangyack and some ultimate plan involving enemies of not only Super Sentai but also of Kamen Riders, what he didn't know was that one Kamen Rider Decade, also known as Kadoya Tsukasa had also heard and was sneaking around a suspected enemy base like Marvelous was when they bumped into each other, having covered each others mouths too so as to not give themselves away, and then got a safe distance away to actually talk when they had confirmed that there was some sort of plan to get rid of both Sentai and Riders

"You heard about this too huh Decade?"

"Yes Marvelous I heard, so...I think we should team up"

"Works for me, how will we do this though?"

"Easy, we kill our respective opposites"

"What?"

"I take care of the Sentai while you take care of my fellow Riders"

"Hold on, I don't want to..."

"Easy, they won't actually be dead, instead I will modify both our weapons so that they're hidden in a pocket dimension until the time is right to reveal the truth about our plans"

"Fine, but only if you're absolutely sure that no one will actually die will I go along with those plans"

"Don't worry I can do that"

"Then I will start with the original Riders while you can take out the Gorangers first I guess, check in periodically to make sure that things are going as planned?"

"Agreed"

"Wait, how are we going to handle any Rider or Sentai that asks about this?, especially my team the Gokaigers, they will never believe what I tell them, especially if I start having to betray them for whatever reson"

"Go with the flow I guess, so you're telling your team about me?"

"Have to once we get started, think about it for a minute and you'll see that I'm right"

"Fine, then let's do this"

"Wait...let's leave at least a few Riders and Sentai respectively out of the dimension just as a backup, we choose respectively who to keep away from the dimension"

"How so?"

"Just decide on a whim, we're the last to fight, and by the way if any of my crew asks about why this fighting has to happen I will tell them to ask Akaranger, forcing them to go to the past but the reality is that it will be me, you can be Rider Ichigo once back at present time"

"Then at least someone from Den-O will have to remain behind because that's the only way for them to falsely get answers"

"Good point, we decide when and where the final battle is to be later"

"Agreed, good luck"

"You too, so there's one other thing I realized we need to do"

"Infiltrate the groups, guess I'm becoming the leader of Dai-Shocker again"

"And I guess I will become the leader of what will be called Dai-Zangyack"

"Here's to hoping this all works out for the best"

"Agreed"

"I'll contact you when I'm ready to modify the weapons"

"Alright, make it fast though"

"Don't worry I will"

Two days later and both Decade's and Marvelous' weapons were modified so that no Rider or Sentai would actually be killed when hit by the weapons when they flashed purple

"So...time to begin"

"Meet you on the field of battle at some point"

"Understood"

After abandoned warehouse battle

"So Marvelous, how are things going on your end"

"Getting there, you?"

"Same, by the way all except two of your team are in the dimension I set up"

"Understood, as you know I mentioned to Joe that he needs to talk to Akaranger"

"So it's finally time, tomorrow then?"

"Agreed, now then there's something we need to discuss quickly before our respective groups get suspicious"

"What's that?"

"Do we pretend to kill each other or not?"

"Pretend to defeat each other, it's the only way"

"I was hoping it wouldn't come to that"

"Unfortunately you know that with that one member detecting Sentai and Rider particles we have to pretend to fall or everything will be for nothing"

"I know, I was just hoping that you could think of another way to trick them"

"Can't think of anything and I doubt you can too"

"You win"

Everything afterwords is the same as the movie