Previously on Let the experiment begin. After Akira putting on some new glasses, he and Ryu meeting with Riser, and watching a rating games between him and Rias peerage. Issei needed some help and so they went into the underworld to stop a wedding by a fight. What will happen next?
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As the fight begins Riser has his fire wings and started flying and uses his fire to attack Ryu and Akira but Ryu uses his flame to counter Riser while Akira felt so useless.

Akira: "Think Akira think what do I have." Then he pulls out the Soujiki Fullbottle

Ryu: "Hey Akira quick question how did you get it?"

Akira: "Short story."

Flashback

Akira was using a vacuum cleaner until it was clogged by something

Akira: "What the?" He checks and finds the Soujiki Fullbottle "Cool."

End of flashback

Ryu: "Ok that was short and boring."

Akira: "Whatever." He shakes the Soujiki and lion Fullbottles which causes math formulas to surround the arena

Riser: "What the-?"

Akira: "Now shall we begin the experiment?" He twist the caps and swap the bottles

Lion! Soujiki! Best Match!

Akira: "Best match? Alright!!!!" He twist the crank

Are you ready?

Akira: "Build up."

Tategami Cyclone! LionCleaner! Yeah!

Riser: "Pathetic eat this!! Then fire were coming towards Akira but he uses the Long Range Cleaner to suck up the fire and stored into the Trash converter

Akira: "Fire!" Then he shoots fire causing Riser to dodge it

Riser: "Is that all?"

Akira: "Ok then Ryu I have a plan."

Ryu: "And that's?"

Akira pulled out the lion for the Taka Fullbottle

Taka! Soujiki!

Akira twist the crank

Are you ready!

Akira: "Build up!"

Then the lion halfbody was replaced with the Taka halfbody

Akira: "Hop on."

Ryu: "What are you insane?!"

Akira: "Trust me."

Ryu: Sighs "Fine." He hops on Akira's back and then Akira flies and handed Ryu the Hawk Gatlinger

Ryu then fires at Riser while Riser just firing fire and while Akira is sucking up the fire

Riser: "Gah! Annoying pests!" Then he charges head on and then Akira replaces the Soujiki Fullbottle for the Gatling Fullbottle

Taka! Gatling! Best match!

Akira twist the crank while in the air

Are you ready!

Akira: He first threw Ryu into the air "Build up."

Tenkuu no Abarenbou! HawkGatling! Yeahhh

Then Ryu does a drop kick on Riser and then lands on the ground and then throws the hawk gatlinger to Akira

Akira: "The laws of victory has been set!." He spins the hawk gatlinger

10!/20!/30!/40!/50!/60!/70!/80!/90!

While spinning Riser was stuck inside of a spherical graph in mid-air

Riser: "No.... You will not beat me!"

Akira: "Yeah Yeah." Then he spins the gatlinger one more time

100!

Then he fires causing the bullets to charge at Riser and ultimately falls to the ground but he was still standing

Riser: "Gah... I am still standing." What he didn't notice was that Ryu was spinning the crank on his driver

Ready go! Draconic Finish

Then a blue and orange dragon appears behind him as he jumps and the dragon breath fire getting close to Riser and then delivering a roundhouse kick at Riser causing him to be knocked out

Sirzechs: "And with that the winners are Kamen Rider Build and Kamen Rider Cross-Z

Then they hear the audience cheering for them

Sirzechs: "Now Tell me what you two desire?"

Ryu: "Well the first thing is that I want you to let Rias marry anyone she prefers and not let some sort of tradition."

Sirzechs: "Deal and what about you Build?"

Akira: "There is one thing I wanted to know..."

Sirzechs: "And that's?"

Akira: ....

To be continued

Next time on Let the experiment begin

Akira: "Something about me isn't right specifically me family."

Sirzechs: "Try not to let your dreams fade out."

Akira: "Night Rouge I want some answers!"

Night Rouge: "Hahaha lets see your improvement."