Reposting from my AO3 account.

The words Gou wanted to say were on the tip of his tongue, but for whatever reason, he couldn't say them as he stared into the pain filled eyes of the man he was holding in his arms. A split second later, he was pushed to the ground.

Time seemed to slow down as he painfully tried to get up, watching in horror as Chase, who had been dying in his arms a moment before, ran toward the disgusting mockery of a Rider that was unfortunately his father. Purple sparks and lightning coursed through the Roidmude's body and as Chase grabbed Banno and started to try to push him back away from Gou, his body began to glow purple.

Gou braced himself to jump up to stop Chase from whatever he was trying to do, but at that moment, the purple light expanded and exploded, forcing the teen to shield his eyes. A moment later, he looked up and his heart dropped to his stomach as he saw the 000 Core that was the only thing left of the Roidmude. His eyes grew wide as the Core shivered and began to spark with the same energy.

"CHASE! PLEASE DON'T! PLEASE HOLD ON!"

He tried getting up, to try to stop the same thing to happen to Chase's Core. If it survived…they could bring him back, give him a new body. Chase couldn't die…not before he had a chance to tell him that…

An energy beam struck the Core, surrounding it within an energy bubble and stopping the explosion that was moments from happening and Gou froze in horror as he heard the insane cackling of his father. Banno appeared in his line of sight, a gold beam coming out of his hand that was attached to the orb that Chase's Core was in.

"Did you really think THAT was enough to stop me? Despite all your little "upgrades", you're still Proto-Zero, still pathetic and useless as my worthless son over there. Still vastly inferior to my finished Roidmudes and my beautiful Sigma Circular. Still… I may be able to use you for one more little experiment. And perhaps…salvage my other biggest failure over there as well."

Gou saw Banno raise his other hand and pain coursed through his entire body, aggravating his previous injuries to a life threatening level. He began to black out, watching as Banno walked closer to him.

—–

Gou wearily opened his left eye, immediately noticing and feeling that the right side of his head was heavily bandaged. An oxygen mask was covering his mouth and nose and as Gou slowly turned his head, noticed that he had a few IVs in his bandaged and bloody left arm, pumping whatever they contained into his body. He had heavy shackles on his wrist, right below his elbow, and right below his shoulder. He surmised that his right arm was under a similar treatment.

His body was mostly numb but he could still feel a few things, mainly the shackles on his body and that there was a sheet covering his upper body. His chest had a dull twinge, like he had a wound there, but whatever painkillers that were no doubt being fed to him through the IVs kept the brunt of the pain away.

"Ah, Gou…so you've finally woken up. Granted it was only about an hour and a half, but I had a limited amount of time and supplies. Still…despite not having the resources I needed, I think I did a decent job with you."

Banno appeared in Gou's vision, next to his head, and proceeded to run his fingers tenderly through the teen's hair. Gou tried to shirk away from the touch, tears pooling in his uncovered eye.

"I admit that I am surprised, despite that explosion, that there were salvageable pieces of Proto-Zero that I could use. I did have to resort to using a few spare Spider, Cobra, and Bat pieces, but your body is remarkably able to adapt to a lot that you're put through. Maybe I should have reconsidered calling you a failure as quickly as I did. Still…if I had, I wouldn't have had THIS opportunity."

"Wh…what…are…?"

"Oh Gou…you're smarter than this, even WITH all the drugs running through your system and impeding you. But, since you can't figure it out…I decided to take my two biggest failures and try to re-purpose you. Basically…combine you. Refit parts of your body with Proto-zero's body."

Gou's eye grew wide and he tried to move his body, move anything, but the numbing agent still in his veins resulted in his task being futile. He started breathing heavily, trying his hardest not to cry.

"Ah ah, calm down Gou! You're only going to exaggerate your heart and make your blood pump faster. I have slowed the blood flow and have been pumping fresh blood in you, but like I said, I have limited resources. But…since you're awake and want to act like this, I guess it's time for the final step. I've already installed the Core Driviar you need next to your heart, now it's time for the Core."

Banno removed the sheet from Gou's upper body before walking away and the teen was glad for the oxygen mask obscuring most of his vision of his open chest cavity clamped with hemostats to control the bleeding. Part of his ribcage had been removed in order to get to his heart and surrounding organs. He saw a glint of metal next to his beating heart that was no doubt the Core Driviar Banno had talked about.

The scientist returned, carrying the orb that had the 000 Core in it, Chase's Core. The Core looked sluggish in the orb, but upon getting closer to Gou's body, it began to try to ram into the sides of the orb. Banno touched the orb, sending a shock through it as it popped, and the Core fell still, twitching feebly in Banno's hand.

"Now, if you two will behave as I do this final procedure, I just MIGHT let you two keep a few of your memories as I reprogram you, mainly the ones where you've worked together. After all, you two need that information to use your new Rider form I've created using those little Signal Bikes of yours."

Gou shut his eye as Banno placed Chase's Core in his chest, right above his heart and the Core Driviar. Tears leaked from his eye as he felt the Core squirm in his chest as Banno attached it to his heart and Driviar.

"There…that wasn't so hard, was it son?" Banno cupped Gou's face gently, wiping his tear streaks away with his bloody hand. The teen opened his eye, hatred oozing from it and he stared as the man above him chuckled and removed his hand. The scientist turned to the machines and pressed a sequence of buttons.

"Alright Gou and I guess now Proto-Zero, I'll have to knock you unconscious again while I finish sewing you up and activating your new systems and the necessary task of rebooting your program and memories. I should think of a new name for you as well. Heh, funny little story for you two. The day I activated Proto-zero was the day you were born Gou. So…in essence, you two are brothers of a sort. Twins even. I guess it was only natural for you two to be combined like this."

The gas in the mask began to smell different and Gou tried his best to not inhale so Banno couldn't finish his work. There was a tingle and a familiar voice joined his conscious thoughts.

"Let it happen Gou. We need rest. Don't worry…we'll beat him. Together."

"Okay…Chase. I trust you." Gou closed his eye, letting the anesthesia knock him out.