"The χ-blade is made from your heart too, idiot!" Vanitas called, brandishing the blade he spoke of. It looked broken—not to mention twice the size of any regular Keyblade. "You destroy it, and you'll destroy the both of us!"

"I know," Ven said, readying his blade. It was a determined whisper more than anything else, and his body trembled. I know.

He'd known since starting this battle that it would come to this, but that didn't change his decision. If that's what it took, to keep Aqua and Terra safe. If that's what it took, to keep Xehanort from getting the χ-blade, from getting Kingdom Hearts, from winning. If that's what it took.

"But can you do it, Ventus?" Vanitas taunted. "Can you willingly destroy your own heart? Hmm? That's a decision a baby shouldn't be making!"

"I've made up my mind," Ven replied. His voice was solemn. His reserve was sound. He wouldn't be backing down. "Are you ready Vanitas? Are you ready to end this?"

"And finally recomplete?" He laughed. "I was born ready, Ventus. Come on!"

Ven ran forward, a gust of wind pushing him along, doubling his speed. Even in the depths of his own heart—or was this Vanitas' heart? Both of ours, I suppose. It's the same heart, after all—he could manage that. Unfortunately, seeing as this space belonged to both of them, Vanitas could call darkness, too. He didn't bother blocking with the χ-blade. He sent a wave of darkness out to drown Ven.

Ven brought up his arms to his head and dug in his heels. The wind whipped around him, even stronger now, trying to form a shield to protect its namesake. It could only do so much, against the darkness his brother commanded.

The thought tugged at Ven's chest. Brother. He'd never considered referring to Vanitas as that until just now, and even now, it hadn't been intentional. He wanted to deny it—him? a brother to this abomination?—but couldn't find it in him to. There was something about the way Vanitas's heart called to him, pulled at him, something in how their hearts reverberated in the presence of each other.

"Can you do it, Ventus!" Vanitas' voice roared above the wind, it sang in Ven's ears. "Can you destroy not just your own heart, but the heart of your brother?" Vanitas' darkness threatened to crush the wind barrier, his presence threatened to smother Ven's heart.

Ven swallowed, reaching within himself, calling not just the wind, but the light that nestled within him. Pulling it out was an effort, like liquid slipping through his hands.

"If that's… if that's what it takes," he said, gritting his teeth and pulling harder. He scooped at the light within him, tugging it out, willing it out. "I'll do anything… to save Aqua and Terra. I'll do anything to keep Xehanort from winning!" The light exploded out of him, banishing Vanitas' darkness—

—except, of course the darkness cast in their shadows, made by his light. With a snarl and a twitch of Vanitas' hand, Ven's own shadow reared up and caught its host by the neck.

"Even if it means hurting me?" Vanitas demanded, golden eyes blazing with fury. The shadow around Ven's neck thickened.

It shouldn't matter, Ven thought, clawing at his own shadow. It shouldn't matter that he's my heart, that he's my brother. I never cared about him before now. I never…

It didn't matter. It didn't matter, whether or not he cared before. He cared now, and he cared so much that it made his chest ache. Doubts swam in his head again. He couldn't do this. How could he find it in him to make the decision to do this—it wasn't just his life on the line, but his brother's, too…

Whatever it takes…

"Whatever- whatever it takes!" Ven choked. "The χ-blade won't- won't save you, Vanitas!"

"What?" Vanitas snapped. The shadow around Ven's neck tightened, but it wavered.

"It won't save you!" Ven repeated. "Xehanort won't- he won't save you, Vanitas! He'll cast you aside once he has the χ-blade in his own hands. You must- you must know that—"

"Shut up!"

The shadow threw Ven back, pulled him through the air, smacked him against the stained glass floor of their heart. Ven coughed and gasped for air, but no more shadows reared up to bind him. Vanitas didn't move.

"He won't… save you…"

"I know!"

Ven pushed himself up, eyes searching for his brother. Vanitas stood there, panting, face contorted with a wild anger. Even in that, his eyes glowed with a fierce determination.

"I know," Vanitas said. "But he's not going to save me. I'm going to save myself!"

He cloaked himself in darkness. Ven dragged himself to his feet, wrapping light around him in the same way.

I wish I could save you, Vanitas. But neither of us can be saved now.

Vanitas ran forward, darkness flying out like whips and snakes, lashing, writhing, snapping. All Ven could do was throw his light back, and pour all of himself into it. His light faltered, wavered, but he pressed on.

Aqua, Terra, please… Lend me strength. I need to end this. I'm sorry it had to come to this. I'm sorry it had to end this way.

The light within him expanded tenfold, and flooded out of him. Through the blur of tears he thought he saw Vanitas rear back, afraid. It didn't deter him. He pulled and pulled at the light within him, pulling until there was none left, pulling until he was dry, pulling and directing it at Vanitas. This was a battle he had to win, no matter the outcome.

Vanitas… I'm sorry, too. I'm so sorry.

Light enveloped him. Vanitas screamed.

AN/ Like my "Aqua is overleveled" fic, this can be considered FtPverse canon, and I personally would call this how this battle happened within FtPverse. However, this was initially written as a standalone piece, and deserves to be posted as such.