What happened to Akira was a unknown but

Starting off with Akira waking up back home where he lived before the universe collided

Akira: He yawns as he looks at the posters of scientists he has on his room "Man today will be great." Then he changes into his uniform as he went downstairs as he sees a note on the fridge

I'll be working a bit late a work. I left some food for you to reheat in the microwave
Your father,

Sento Kiryu

Akira: "Well that's not unusual." He sighs and walks to school "Though I wonder if there is something supernatural about this world that I'm not seeing. Hmm..." he kept thinking "Eh I don't think there is that much supernatural stuff besides I'm a man of science not an occultist." Then while walking to school he was approached by Sona

Sona: "Ahh Mr.Kiryu there are somethings I must discuss with you."

Akira: "And that's?"

Sona: "Well for once you are cleaning the school after school for yesterday's incident."

Akira: "Yesterday?"

Flashback

Akira was the president of the science club which means some stuff were about to go down and one day while he was teaching on explosive he created a concoction which were explosive to which he threw it to the student council room on accident

Sona: "What the-?!" Then the concoction exploded which luckily it didn't contained anything for it to explode but it created a huge amount of foam in the room which surprised everyone in the room

End of flashback

Akira: "Well then again at least nobody got hurt." He laughs

Sona: She facepalm "You know you caused a huge mess!"

Akira: "Well i'm sorry about it."

Sona: She sighs "You know that won't get you anywhere. Besides you still owe that date."

Akira: He sighs "Fine." He mumbles "That'll hinder my work but whatever." Then the went their separate ways as he went to class and sees his 'childhood' friend

Ryu: "Hey Akira."

Akira: "Oh Great hey Ryu do me a favor."

Ryu: "And that's?"

Akira: "You see I need help cleaning after school."

Ryu: "The whole school?"

Akira: "Yep."

Ryu: "Well i'm not busy today and plus Akeno will be busy so sure."

Akira: "Alright I knew I can use you for something." Then class starts "Though it's weird that I have no idea how I got into dating with her." He just didn't mind and just paid attention in class

Later

As his last class ended Ryu and Akira went around the school cleaning which got some help from Itsuki and Hygami

Hygami: "So another lab explosion?"

Akira: "Replace lab with student council room and you're right."

Itsuki: "Wow dude you really are an insane scientist."

Akira: "Hey I'm a genius at least I knew it was just a foam explosion and not some bomb."

Hygami: "That makes the situation less worse."

Akira: "Well I should head out besides it's not like she'll find out." Then he walks out of the school where Sona was waiting for him

Sona: "So you finish cleaning?"

Akira: "Nah I let someone else doing the work for me. One person I ask while two others wanted to help out."

Sona: "Wow that's being lazy."

Akira: "Well I don't care. Let's just get this date over with."

Sona: "Fine."

After one date

After their date was over the went back home but Akira was taking a long route

Akira: "Huh it's weird how did we even met. In fact how do I know those three guys?"

???: "Welcome to another world. Akira Kiryu."

Akira: "Huh?" He looks up to see Destroyer

Destroyer: "Do you remember who I am? The one that separated from you?"

Akira: "Gah!" He has a headache and then remembers everything "Destroyer?! What's going on. Where are we?!"

Destroyer: "This is what happens when the power of black and white hole collided, it resulted in being a world where there is no supernatural. Meaning everyone here is human."

Akira: "Is there a way to get out?!"

Destroyer: "There is. As when I notice you were here it shows that the universe can't contain two same people at the same time. One of light while the other of darkness. I know it sounds like some anime crap but go with it. You see in order for one of us to get out and be brought to the real world we have to kill each other until one remains."

Akira: "So then I guess that means..."

Destroyer: "Yep so that means i'll be the one to kill you and destroy this miserable planet with the science you created."

Akira: "Science was never meant for the use of destruction of others. It was meant to help people!"

Destroyer: "Help?! Look at yourself you were born from the devil of a scientist, you were the one who kept failing of stopping an unstoppable monster, and you were the one that created me!!!" Then he pulls out his gun and the black hole magazine "Now shall I begin the final experiment on my test subject." Then he inserts the magazine to his gun

Over the Revolution!

Destroyer: "Revolution Chaotic upgrade!" Then he press the trigger

Black Hole! Back Hole! Black Hole! Revolution! Fuhahahaha!

Akira: Then he pulls out his driver with the white hole trigger inserted and springer with the rabbit bottle already inserted "Now shall we begin the experiment?"

Hop! Springer!

Then he twist the crank

Are you ready!

Akira: "Henshin!"

White hole! White hole! White hole! Evolution! GOOO!

Akira and Destroyer went at each other as the two were able to create destruction in their way as Akira was going on the offense

Akira: "I will show you the true meaning of science!"

Destroyer: "I'll show what kind of power science can be used!" Then suddenly the two's power were so strong that they struck there own black hole/white hole item as then they break and they downgraded to their next form

RabbitRabbit! Yabei! Haei!

Supuringā! Yeah!

Then the two kept going at each other which Akira couldn't match the speed of Destroyer as he over powered him which caused Akira to downgrade to his next form

Genius! Sugei! Monosugei!

Then Akira kept attacking as then Destroyer and Akira brought each other to their next form

RabbitRabbit! Yabei! Haei!

TankTank! Yabei! Tuei!

Then the two kept fighting over and over as Akira had the speed advantage so he kept striking and that was when Destroyer knew his pattern and grabs him and fires a energy blast with his gun at him which was powerful to downgrade him

TankTank! Yabei! Tuei!

Then the two were equal as Akira was able to bring him down and kept attacking but Destroyer was smart and used the energy blast to shoot him but Akira does the same and Destroyer and Akira downgraded

RabbitTank Sparkling! Yea-Yeahhh!

RabbitTank... Fire the best match!

Then they kept attacking as Akira was using his drill crusher but then the two performs their rider kicks at each other which resulted a draw as they downgraded once more

Rabbit...Fire!

RabbitTank! Yeah!

Destroyer: "Looks like we have reached to our first form. And I shall show you-" Then Akira laughs "What's so funny."

Akira: "Oh come one 'we' aren't giving up." Then he removes the bottles as his rabbit bottle turned gold as he somehow pulls out the dragon bottle as it turned silver as he inserts them onto his driver

Rabbit! Dragon!

Then he twist the crank

Are you ready!

Akira: "Build up!"

Best match!

Destroyer: "Not even a best match and you'll be using that? HA!" Then the two kept attacking as Akira was able to overcome his attacks as Akira then pulls out the Phoenix bottle which changed color from red to a light shade of pink as he inserts it onto his driver

Rabbit! Phoenix!

Then he twist the crank!

Are you ready!

Akira: "Build up!"

Best match!

Destroyer: "Another best match!?"

Akira: He smiles "Do you really think I would have one best match?" Then he attacks as he then shoots fire at him as he attacks Akira while moving fast

Destroyer: "ENOUGH OF THIS GAME!!!"

Akira: "Fine then." Then he pulls out 3b and inserts a empty bottle "Now shall we begin the final experiment?"

3B!

Then Akira inserts the 3B onto his driver

United!

Then Akira twist the crank which there were three pipes one blue, one red, and one dark pink

Are you ready!

Akira: After he kept thinking of everyone back in his world "Everyone...thank you for all the help you given me...BUILD UP!" Then the three pipes formed into one

Saidai no nō! Massuruheddoburaun! Fumetsu no bi! Kamen Rider United! Cross-Z Build Phoenix! Yeah! (The greatest Brain! The musclehead Brawn! The immortal Beauty! Kamen Rider united! Cross-Z Build Phoenix! Yeah!)

Akira: "The formula for victory has been set!" The armor comprised of his legs having the rabbit side, the fist having more of the dragon side, the red coloring and the feathers on his back of the phoenix side, and as the eyes were similar to the rabbit side

Destroyer: "This is it?!" He laughs "I'll tear down your best matches to nothing." Then he charges at Akira but Akira dodges as his punches were devastatingly strong as he twist the crank

Dragon! Ready go! Draconic Finish!

Then Akira does the rider kick of Ryu as he leaps in the air and a dragon made of blue and orange energy as he lands the kick on Destroyer

Destroyer: "GAH!!!" Then Akira twist the crank

Dragon! Phoenix! Ready go! Burning finish!

Then Akira leaps in the air as wings made of fire appears on his back as he flies in the air and then goes for a dive kick causing Destroyer's rabbit lost bottle has a small cracking causing for Destroyer for him to weaken and Akira twist the crank once more

Dragon! Phoenix! Rabbit! Ready go! vortex finish!

Then Akira does his normal vortex finish by having a graph trapping Destroyer as then Akira leaps in the air and then goes for a rider kick as Destroyer's bottle had more cracks

Destroyer: "DAM IT!!!" Then Destroyer press the trigger

Steam break! Rabbit finish!

Then Akira twist the crank

Dragon! Phoenix! Rabbit! 3B! Ready go! 3B finish!

Then Akira does his rider which had the power of the three riders as the two kicks collided with each other

Destroyer and Akira: "HAHHHHHHHH!!!!!!!!!!!!!!!!" Then Akira pushes forth

Destroyer: "HUH?!"

Akira: "TAKE THIS!!!" Then his kick proved more powerful as he kicks Destroyer and his bottle breaks causing for Destroyer to explode and vanish into thin air and then Akira's hair color went back to normal "It's over..." Then Akira's armor disappear and then a portal opens "I guess he wasn't wrong." Then he enters back to his world where it was night and he sees that everything was back to normal before the destruction of Team Dark Build "Wow that was quick." Then he walks to school for no reason

Later

Akira kept walking as he notice a door open to find Ravel still crying for what appears to be the lost of Akira

Ravel: "Akira...sorry...I hope you're doing well in the afterlife."

Akira: "Wow you know if you kept losing onto hope then you won't know what it feels like to express joy."

[There should be a GIF or video here. Update the app now to see it.]

Ravel: "Huh?" Then she turns around to see Akira

Akira: "It's been a while hasn't it Ravel." Then she hugs him tightly as she started crying uncontrollably

Ravel: "Idiot! Do you know how worried I am about you! I thought you were dead!"

Akira: "Yeah well i'm alive and back to normal."

Ravel: She stops crying "Hey Akira you know that I still loved you even though already a three days passed by."

Akira: "Wait three days?!"

Ravel: "Yeah. Can you answer me something?"

Akira: "Yeah what is it?"

Ravel: "What do you see as?"

Akira: Then that was when he goes for the kiss as she was surprised "As my girlfriend of course."

Ravel: "Well that's what I wanted to hear." Then they heard the other members from team build to which she had and idea and for some reason her twin drill hairstyle started to spin like how a drill does

Akira: "Eh?" Then Ravel grabs him and they ran out of the school

Ravel: "Come on! Take out your bike."

Akira: "Umm sure." Then he pulls out his phone which morphs to his bike as then Akira and Ravel hops on and Ravel gave directions to a hill to see the moon

Akira: Then he shows her the script

Ravel: "What's this?"

Akira: "It's another script. It's all on the adventure after the two worlds collided." Then he took out his phone and plays and epic background music "Kuoh once home to Kamen Riders who only two were left which were Kamen Rider Build Akira Kiryu and Kamen Rider Cross-Z Ryuken Geki."

Ravel: "Hey why are you trying to give an introduction."

Akira: "It's just for reason. Anyhow after living in this world we try to get used with it until that was when a alien name Killbus, a terrorist name Felix, two cyborgs name Kaiseis, and a doppelgänger name Destroyer as the Genius tries to reunite team build and as well with the memories he lost."

Ravel: "And after the defeat of Killbus, Felix, Kaiseis a day later and Evolto grabs the pandora box and promise one day to come back to Earth to destroy it. And as time went on everyone went to go through their normal lives but hard for Team Build to deal with the lost of their Genius they rely on."

Akira: "See told you that worked perfectly."

Ravel: "Yeah and also are you gonna tell the others about it."

Ryu: "Nah because we heard everything." Then that was then the rest of Team Build appears

Akira: "How long-"

Ryu: "We saw you guys running away so we followed you."

Akira: "Well then I guess this is the end for good."

The End!

As one story ends another opens

As a man uses a device and press the button

Mighty Action X!

???: "Henshin!" Then the person transforms