Spoilers from included and/or represented works abound. Please read this fiction carefully.
"Look, do you really exist, or are you just a person that never really was, despite having known your friends?" Shadow Kotone asked.
"Persona!" Kotone Shiomi took her Evoker and summoned her Persona, female Orpheus.
"Let's get dangerous!" Ryuji Sakamoto (Skull) charged up.
The Persona users summoned their respective Personas, and, except for the Phantom Thieves of Hearts and Fuuka Yamagishi and Labrys, went directly against their false Shadows (who're copies of their true Shadows). Tohru Adachi, with his Persona Magatsu-Izanagi, and the Phantom Thieves assisted.
"Another shits taking place in another world." Adachi commented.
Strike got summoned as well, and...
"Sweety Bo-beety, I'm back!" Strike recognized K.O., then took his blaster.
"Not you again!" K.O. is less than thrilled.
"And more heroes equals more bust!" Strike then went around without hesitation.
"You're not getting away!" Shinra and Ouma agents took the fight alongside K.O.
"Thanks, Mister Alice!" K.O. thanked Reiji.
Prometheus, by the summon, automatically created a very large portal behind him. The God-Scientist and his creature emerged from the portal.
"What!?" The rest of the alliance is shocked.
"A scientist!?" The Radical Six is shocked.
"Behold, my punky creation, a machine-loaded girl designed to destroy the Keystones!" The God-Scientist introduced the creature.
"Break the Keystones." The creature said.
"She looks like a cyberpunk loli." Kai commented.
"Is she really as young as she looks?" Chloe questioned. "Then again, she looked quite broken and depressed."
"Wait... is she...?" Lucy noticed.
"What?" David then looked.
Same short statures, same distinctive skull iconography of her tattoos, same neon pink and blue color scheme, same light green hair, same iris and sclera, even the patched version of the same outfit... Only difference there are mechanical patches on her body laterally, dark circles, and her hair worn down and messy.
"R-R-Re... Rebecca..." David recognized her.
"You're her?" Lucy realized who she is.
The creature is actually Rebecca came back to life, patched with mechanical prosthetic parts and technologies from multiple worlds, armor being made of the same metal doing in the Origin. The right hands is the same golden cyberhand as previously equipped by her late brother, Pilar.
"What's wrong, Mr. Cyberpunk?" York Neely/Yuuto Kannagi asked David. However, David did not respond.
"He is not talking right now." Mikoto 'Miko' Aiba noticed.
"As if he's facing a crisis..." York commented.
"Rebecca... is back." Lucy revealed.
"What!?" Team Baku is shocked.
Rebecca then took out the hyper-charged copy of her signature shotgun, 'Guts'.
points the shotgun at David and Lucy* "Die." Rebecca is then pulled the trigger.
Adam Smasher then subconsciously activated Sandevistan and perfected David and Lucy altogether, taking the shot.
"Why do you interfere?" Smasher questioned.
"Adam Smasher!" Team Baku is surprised.
"Ugh... Not a normal shotgun..." Smasher is visibly injured and damaged.
"That freaking shotgun must have some powerful magics in each shot..." York suspected that the shotgun is imbued with some magics.
"Alright! We'll chase Prometheus!" Tenma Jumpson reassured.
"Let's catch the Keyman!" Captain Velvet Meteor ran alongside.
"Good luck, you two!" Touya Ijuin/Troy blessed both.
"May the Baku bless you all!" May blessed both.
"Hmph. Foolish lowlifes." Prometheus and the God-Scientist then both retreated inside the portal, but Tenma Jumpson, Captain Velvet Meteor, the Forger family, the Princess and EX, the Slime, Chloe Love and Kai Iod, Gabimaru, Hibino Kafka, Chrome, Ushio Kofune, Son Gohan and the Hegemonies chased.
"Rebecca... So you're back but..." David is in crossroads.
"David... You're not the only one at that kind of loss..." Lucy told David. "Because you sacrificed yourself to save me and allow me to reach the moon in the future back then."
Rebecca is about to shoot again, while Smasher is shielding both.
"Wrong world, baby!" Three cyberpunks drop-kicked Rebecca, knocking her away.
"Silverhand!?" Smasher recognized one of them.
"Argh!" Rebecca fell down, dropping the hyper-charged shotgun.
"Silverhand here. Good thing I learned from the infos." It's Johnny Silverhand! "Alternative timelines, alternate worlds, whatever."
"Is that those!?" Mickey Mouse and friends approached the threesome.
"We have two V's there." Silverhand revealed.
"Oh wait... It's Valerie and Vincent!" Sora recognized V.
"You're David Martinez from Santo?" Vincent asked David.
"Huh? How do you know?" David asked back.
"A certain drink with your name in it." Valerie replied.
"Who're you, V?" Mickey Mouse asked.
"These are two possible punks for me, Valerie and Vincent. They came from another timelines." Silverhand introduced V. "Apparently, they got such in a certain variation of the same kind of time loops miss Kofune experienced."
"You mean... Ushio Kofune!?" Lucy is shocked. "A blonde Shadow with a human heart!?"
"More augmentation, done to accommodate the magic usages and needs." Silverhand continued. "For all three of us."
shows a Space Stone* "Without such enhancements, we wouldn't have been able to access here with the Space Stone." Vincent continued. "We would've lost control of it quickly."
"You're basically the many variations of the legendary V!?" Lucy is surprised.
"You read our stories?" Valerie asked back.
"You, why did this girl I used to have killed trying to kill all of us?" Smasher asked.
"Firstly, it's complicated. Secondly, that scientist brought her." York explained. "And finally, Prometheus is trying to wipe us all out."
"Prometheus?" V and Silverhand has no idea who Prometheus is.
"We'll talk about it later." Troy them focuses on battle.
"I'm sorry we have to fight you..." David looked at Rebecca.
Rebecca then stood up and telekinetically grabbed the hyper-charged shotgun, and then frantically shot them all. The cyberpunks (so Smasher now works with his nemesis, Silverhand), Sora, Mickey Mouse and friends, and team Baku then dodged and went combat. The Persona users is still fending off the Shadows, some Jump and the Hegemonies chased after Prometheus and the God-Scientist, while the rest of the alliance is fighting Strike.
"Wow wow wow!" Zero the girl is watching everything from afar. "Those nemesis actually worked together against my pawns!"
"Empress Zero, the supreme baggage has successfully been prepared." Rigna the Bloodrunner reported.
"However, Angela of Lobotomy Corporation has been captured by that alliance." The mysterious woman, who's clad in greyscale, reported. "The attempt to bring the Cross-Dimensional Observation System No. XX has failed miserably."
"You should've just killed Kouha, Fusion!" Rigna complained.
"Rigna, Union... Go find something." Zero the girl commanded.
Rigna and Fusion both bowed, and then left.
Back in Logjam Nexus...
"I can do Shadow works." Shadow Makoto Yuki exclaimed.
"What are you thinking? Toying with people's lives and deaths?" Makoto Yuki questioned his doppelganger.
"Once you die, you'd regret your death and the prevention of the potential accomplishment of your future." Shadow Makoto Yuki explained. "Once you're dead and don't come back at all, your future is lost."
"No!" Makoto Yuki rejected, then slashes his fake Shadow.
"Also, you're not real." Ren Amamiya (Joker) then shot the Shadows. "You're all just false copies with no heart for us to steal!"
The Investigation Team then summoned their ultimate Personas.
"You think you can stop us?" Yu and charged ahead.
The Investigation Team then finishes off their fake Shadows. The members of S.E.E.S. also did the same to their doppelgangers.
"Nooooo!!!!!!!!!!" The Shadows finally melted away.
"Yes! Finally!" Kanji rejoiced.
"Good job, you guys! Shadow Operatives don't falter!" Labrys congratulated the Persona users.
"Here's something you'll want to drink." Yu gave Labrys the same drug David and Kouha/XX used. "You did well, just like we did."
"Yuka-tan, do you want a group selfie?" Junpei asked Yukari.
"Finally! The Shadows are all gone!" Ken is relieved.
"Let's join the fight against..." Yosuke suggested.
Then Labrys is suddenly shot.
"Labrys!" The Persona users saw it, and approached.
"Ugh... Who shot me?" Labrys is fuzzy right now.
The Persona users then looked at Rebecca, who's approaching them.
"Rebecca's going to kill us!" Miko shouted.
"Miss Aiba! We're coming!" The Investigation Team then charged ahead. Members of S.E.E.S. as well as the Phantom Thieves and Labrys followed.
"Stop!" The Personas quickly restrained Rebecca.
"You!" Rebecca is stuck.
"Rebecca is trying to kill us." David explained Rebecca. "I know her. She's in the same crew as mine back in our original lives."
"I feel bad for her..." David then sighed.
flashback of David's moments with Rebecca*
"Oh. A girl older than she appears?" Yu then tried to calm Rebecca down. "Hello, you cute missy."
"I'm Unit #31, the experimental anti-Shadow weapon, redesigned into human." Labrys introduced herself. "I'm Labrys, student council... well, nice to meet all of you."
"I'm Johnny Silverhand." Silverhand introduced himself. "And this is Valerie and Vincent."
The Persona users then introduced themselves.
"Let's go to help people fight the so-called... Strike." Sophia suggested.
"We'll escort this girl!" David assured.
The cyberpunks then carried Rebecca amd the hyper-charged shotgun before she could react, while the rest came to assist in fighting against Strike.
"Why won't you yield!?" Strike frustratingly beats up some fighters.
"We could ask you the same." Bahn punches Strike.
"Ugh! But at least I cannot leave my blaster alone!" Strike then setup his blaster.
"You have no right to mark us with strikes!" Reiji, Xiaomu and Saya pointed their guns towards Strike.
Strike simply shot overhead, summoning in the sky some more... Warriors of Light.
"Look up." Strike told everyone. "Someone's falling."
The Warriors of Light fell down on top of everyone near Strike. However, a black one then teleported into where the mysterious sword as wielded by Loid's informed wife, the assassin Yor Briar.
"Oh, sorry." That one apologized to Yor.
He took the sword front her and started analyzing it. Strike wasted no time, floating in the air now, setting to instantly incapacitate the one by turning them to stone through firing the blaster.
"I'll stop you now!" Strike shot at the one...
... only for the latter to notice and the. successfully bisecting the projectile by cutting with the sword, saving him.
"H-h-how!? How could you cut my projectile!" Strike is shocked.
"Sorry, my people's clients from other worlds, for interrupting." The one apologized to everyone.
"Who are you?" Yor asked that one.
"I'm Noctis Lucis Caelum, the king of Lucis." The one introduced himself. "Why do you care about Shinra?"
"What Shinra?" Xiaomu is confused.
"Hey, the name's the same!" Cloud Strife noted.
"What do you expect, mister?" Noctis asked Strike.
"Sorry for inconvenience." Sheath apologized to everyone. "The Warriors of Dissidia has been teleported by some certain threat, please underst-"
Strike shot Sheath mid-sentence, incapacitating her. Resulting in the stone statue as her body, with a red 'X' on her body.
"You...!" Saya noticed that, and non-hesitantly headshot Strike.
regenerates his head* "You're so stupid." Strike mocked the alliance.
"Strike! You're so terrible!" K.O. knew it. "I should have used the blaster to kill you back then!"
laugh* "Now you have remembered, Sweety Bo-Betty!" Strike responded.
"You're a danger to the omniverse." Meden told Strike. "I knew Empress Zero would like you."
"Sure she do!" Strike confirmed. "After all, I'm along the chosen!"
"Chosen of the Broken." Tales of heroes responded.
"You're far worse than my pitiful family." Kazuya transformed into his Devil form.
"I should have summoned Shinryu first!" Strike hastily summoned Shinryu.
"Not Shinryu again!" The Warriors of Light and Oros Phlox is shocked.
"How about... Cross All?" Stephen Strange suggested.
"Let's bring CN City into the mix." Strange Supreme then create a portal in the sky, revealing CN City.
"Mirror... Phase Shift." Both Strange used the spells, shifting CN City with the Mirror Dimension. Various versions of Ben Tennyson fell to the battlefield.
"Ben! It's you... and you and you and you and you!?" K.O. is surprised. "Wow! And more!?"
"Oh shoot!" Alien Force Ben then stood up. "What just happened?"
stands up* "Look, dude, we meet again." Omniverse Ben told the other versions.
stands up* "Oh... wait." New Ben saw K.O.. "It's you!"
"Oh, Ben, you're back!" K.O. recognized the new Ben. "Oh, I missed you!"
"Ben Tennyson! Help us!" Strange told Ben. "Shinryu is trying to kill us all!"
All versions stood up. Ultimate Alien Ben is confused by what's happening right now.
"Is there's more?" The original Ben asked.
"Look!" Gwen Tennyson told everyone.
Gwen 10, Ben 10K, both Uncle Max, and Ben 10,010 all fell too.
"Summoning Ben Tennyson and his family?" Strike mocked the alliance. "I got wise, as I don't allow you to steal my blaster!"
Strike then flew straight up towards space, leaving Shinryu to the work, charging Xenoflare. At that point, Ben Tennyson and family got to band together.
"The hero of heroes is back!" Ben 10K got up.
"Finally, more family meets more friends!" New Ben exclaimed.
"As you wish, Ben Tennyson." Kogoro and Mii replied. "Now, activates your weapons and Omnitrix!"
Gwen took the Omnitrix, and then all Ben Tennyson and both Gwen activated their Omnitrix.
"How do we Cross All?" Kyo Kusanagi asked.
"Wait a second..." Deadpool noticed.
Note: 'Cross All' refers to a finishing move involving several fighters doing it together by charging ahead while being imbued by powers and energies. This otherwise unnamed move is present in the openings of Namco Capcom and both Project X Zone and Project X Zone 2.
"Hngh!!!" Deadpool then shouted.
Everyone at the fight then gathered energies and powers conspicuously. The Omnitrix wielders, in particular, ended up being engulfed with green light.
"Finish it. In one strike!!!" The alliance then charged ahead and empowered with all their powers, through Noctis now also took the mysterious sword. "Cross All!!!"
The alliance quickly overpowered Shinryu, and killed it before it could finishing charging the Xenoflare, the same attack Bahamut fired after the Power Rangers was blackmailed. But it doesn't end there.
"Take this, Ben Tennyson!" Noctis threw the mysterious sword to new Ben.