When I finished binge watching the second season of Voltron: Legendary Defender with my roommate, we were so freaked out about Shiro's mysterious disappearance that we immediately started speculating as to what happened to him and why he disappeared from the cockpit of the Black Lion. Since I'm a huge Red Rising fan and I wanted to add some more fanfics to the archive for it here, I decided to combine one of my theories on what happened to Shiro with Pierce Brown's amazing Red Rising trilogy and present my idea as a crossover.
Disclaimer: Voltron: Legendary Defender and Red Rising belong to Dreamworks/Netflix and Pierce Brown, respectively. I own none of this.
Update 11/4/17: Due to some story ideas I came up for the sequel with that necessitate rewriting the back half of this fic, I'm going back and doing a complete overhaul of the story to flesh things out and make things better. The original prologue was a fast forward to the Iron Rain in the last third of this fic, but I decided to rework it into Shiro's perspective of the last few minutes of the Voltron vs. Zarkon fight, since the sequel starts with Keith's POV of the aftermath.
Prologue:
Zarkon's Central Command
2037
"Keep Zarkon away from the Black Lion!" Pidge's voice was faint as Shiro slowly regained consciousness. Zarkon had tried to take control of Voltron through what little remained of his bond with the Black Lion, and the last thing Shiro remembered before passing out was Zarkon blocking Voltron's attack and sending a burst of energy through his whip that forced the lions to separate. Shiro took it as a good sign that he was still alive. It meant that Zarkon hadn't gotten his hands on the Black Lion yet. Hearing Pidge's voice also meant that the rest of his teammates were okay.
"Come on!" he heard Keith shout as the ringing in his ears began to fade. "We can't give up." Shiro's eyes widened as he fully woke up, looking out the front viewport of the Black Lion to see the rest of his team firing everything they had at Zarkon and his Voltorn-sized armor.
"I'm running out of strength, man," Hunk called out over the com. Shiro lurched forward in his seat as Zarkon brushed off the stream of lasers surrounding him. Come on, he said to the Black Lion through their bond. Let's get back in this fight.
"Look out!" Lance shouted as Zarkon lashed out with the whip on his massive suit of armor. Pidge's and Keith's screams echoed in his ears as movement to his right drew his attention. A panel on the console was rising, revealing the port that his teammates would plug their bayards into in order to activate new weapons and abilities for Voltron. In an instant, he knew what the Black Lion wanted him to do. If they were going to defeat Voltron, they would need Zarkon's bayard. And Shiro knew just how to get it. As Zarkon continued to wipe the proverbial floor with his teammates, Shiro pushed the Black Lion forward, her memories of their bond flashing through his mind as Lion and Paladin surged toward the Galra emperor.
He felt a surge of quintessence on the lion's back, and though he couldn't see outside the Lion's field of vision, he knew that he had unlocked her wings. The Black Lion glowed with pure quintessence as she moved at hyper speed, passing through Zarkon's armor in a beam of light. For a moment, Shiro was back in the astral plane moving fast through Zarkon's form before he was back in the Black Lion's cockpit an instant later. As he felt his lion's wings dissipate, he felt the weight of a bayard in his right hand.
"Whoa!" Lance exclaimed over the comm. "What'd you do?"
"I've got Zarkon's bayard," Shiro explained as he lifted the device up, so he could get a good look at it. When he did, it shifted from the harsh, angular form Zarkon had corrupted it into, back to the standard default form of the other ones.
"You mean you've got your bayard," Keith corrected proudly.
"We've only got a few minutes left before power returns to Zarkon's ship," Shiro said, switching back into battle mode once more. "Form Voltron!" Gears shifted, and mechanical limbs rearranged as Shiro felt his lion converting into the torso configuration. He could feel the other lions connecting to his through his bond with Black seconds before the indicator lights lit up on the control console. Within seconds, Voltron floated in space, facing down Zarkon from across the distance between them. He could feel his teammates' emotions through their bonds with their respective lions. Their relief that everyone on the castle was alright, and their unyielding resolve as they charged into battle, five minds moving as one.
Again, and again Voltron and Zarkon clashed like medieval knights jousting with lances, each strike accompanied by a blinding flash of light as their blades locked. Coran reported that power was returning to the Galra command ship as Voltron launched another blow at Zarkon, only for the Galra emperor to block it once more. They wheeled around and chased after their foe again, Keith and Pidge raising the sword into a ready position as they flew.
"This is our last chance," Shiro reminded the team. "Let's finish this." With one last battle cry, Lance, Hunk, Pidge, and Keith all surged their controls forward in unison as the blade impacted against Zarkon's armor. When the flash cleared from their eyes, pink crystal fragments floated in the space between the two metal titans, drifting up from where Voltron's sword had pierce the belly of Zarkon's suit. In a last attempt to destroy the Paladins, Zarkon brought his suit's arms up to Voltron's head and sent a surge of electricity through the defender of the universe. Shiro flinched in his chair as the energy raced up his arms. He fought the surge enough to see the open slot for the bayard still illuminated, and with a groan of pain, he fought through Zarkon's attack and plugged the bayard into his slot. He turned it like a key in an engine and Voltron's sword burst into flames.
Keith brought the Red Lion up and drove the blazing sword deeper into Zarkon's armor, sending tendrils of golden lighting shooting out into the space around them. The team let out one last battle cry as they pulled the blade free. The team pulled back as Zarkon's battle suit sparked and twitched. And finally, the emperor's armor exploded in a titanic explosion that filled Shiro's vision. But as the light faded, darkness crept over him, and consciousness left him.
This fic is set during Golden Son, the second book in the Red Rising trilogy. While this fic mainly follows the plot of the book, Shiro's presence will cause some major changes towards the end, particularly in terms of character deaths and shifts in allegiance that happened in canon but will be prevented here.
Although I will try to avoid going into too much detail about the Red Rising universe to encourage people who haven't read the series yet to get started, I will at least provide some basic information for the sake of comprehending some of the background things characters are talking about, particularly since the books never really provide a glossary of all it's terms.