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Katsuki snarled and lifted his weapon again. Izuku fell back into a defensive stance, ready to fend off the next wave of attacks, but they never came. Izuku heard a loud gagging sound, accompanied by the clang of a Keyblade hitting the ground. Instead of fighting, Katsuki was on his knees, hands cupped over his mouth like he was trying to keep something from spilling out. "Damn it, not now ," he hissed, his voice rough and hoarse.
Izuku took a hesitant step forward, hand outstretched. "K-Kacchan? Are you-"
" Stay the hell away from me, Deku ," Katsuki growled, and for the first time in a long time, Izuku felt that once-familiar jolt of fear through his heart. Katsuki's eyes were unnaturally bright and fierce, and with every vicious word, Darkness bubbled up from his lips, dribbling down and coating his chin and neck in the thick, tar-like substance. " Just stay the hell-"
Katsuki cut himself off with a series of hacking coughs, more and more Darkness spewing forth, until it rose up and swallowed him whole before Izuku's horrified eyes. " KACCHAN !" he shouted desperately, falling to his knees next to and clawing the puddle that had previously been his one-time friend. " KACCHAN!"
A gurgling, hissing spit sounded behind Izuku, and he slowly turned his head to see Katsuki staring at him with wide eyes. Wide, empty, glowing white eyes that contrasted horribly with the the viscous inky Darkness dripping from him. He looks like a Nomu . The thought alone nearly made Izuku nauseous. " De-ku. " The word was strangled and furious in not-Katsuki's mouth, and Izuku instinctively took a step back, his grip tightening on his Keyblade.
"K-Kacchan?" he called, trying to keep his voice from trembling. "Can you hear me in there?"
The not-Katsuki paused for a moment, his head cocked to the side like a dog listening to a call. For a moment Izuku thought he'd somehow gotten through, but then the not-Katsuki crouched low, his teeth bared and leapt forward. He slashed wildly with long claws, and Izuku noticed distantly that Ground Zero was nowhere to be seen. But he didn't have long to think about that because the not-Katsuki's attacks just kept coming. Izuku knew how Katsuki fought. He'd been watching him his whole life, and fought against him several times since coming to UA. This wasn't how Katsuki fought. The blows were blindingly fast and more powerful than ever, but they lacked Katsuki's finesse. The moves weren't sloppy, Izuku doubted Katsuki even could be sloppy, but they were all attacks made solely for that moment, with none of Katsuki's two steps ahead style. Which is what gave Izuku his opening.
Izuku landed the flat of his Keyblade against the not-Katsuki's gut and flung him as far away as he could. " KACCHAN, LISTEN! " he shouted, ignoring the way his voice cracked in desperation. "I don't know what's going on with you, but you have to fight it! Please, Kacchan!"
"De- ku ," the not-Katsuki spat. The word sounded almost gurgled behind the Darkness overflowing from his mouth. He leapt forward again, and Izuku was back of the defensive. "Think you're… better than me ," he rumbled. "Always looking… down. "
Izuku almost dropped Deku in his shock, which gave the not-Katsuki the chance to knock him away. "I've never thought I was better than you, Kacchan," he swore as he righted himself. The not-Katsuki was stringing together words, which had to be a good thing, right? He just needed to find Katsuki in there. Reach him somehow. "How could I? You were the one in my life, shining as brightly as every Hero of Light we ever admired. How could I look down on you when you were my symbol of victory?" He shook his head and gritted his teeth before falling back into his attack stance. Katsuki didn't listen to words when he was in full control. There was definitely only one way to talk to the not-Katsuki. "And that's why I'm going to beat you, Kacchan. I'm going to make this Keyblade my own, and I'm going to win against the person who matters most. Maybe not today, maybe not even tomorrow, but I will."
The not-Katsuki stood still for a moment, visibly trembling before letting out a world-shattering screech. Izuku ran forward, and brought his Keyblade around in a heavy swing directly to his chest, sending him flying up in the air. Izuku switched quickly to Uravity to jump high in the air, then straight to Ingenium for a hard downward swing. " SMASH! "
The not-Katsuki was back on his feet before Izuku and they fought trading blow after blow, neither quite pulling ahead. Until the not-Katsuki finally got Izuku pinned to the ground, knees digging into his thighs, wrists grasped tightly in one big hand, and teeth bared at his throat. Izuku tried summoning his Keyblade to his hand, but the not-Katsuki snapped his teeth in a snarl, and slammed his hands to the pavement, and Deku vanished back into light. The not-Katsuki moved in closer, and Izuku flinched and turned his head away, eyes screwed shut. If he was going to die by Katsuki's hand, he at least wasn't going to watch it happen.
"I win."
The words were sharp and clear, and Izuku's eyes snapped open to look up at Katsuki. There was still the tar like Darkness clinging to him in thick patches that dripped down and disappeared before they hit the ground, but his eyes were bright and red. "Kacchan," Izuku breathed.
Katsuki bared his teeth again. He pulled back his free hand and summoned Ground Zero, the end pointed directly at Izuku's chest. "I'll kill you Deku. I'll kill you if you even think about-"
"Stopga."
Izuku froze at the familiar voice, but it wasn't out of fear of being caught. Yagi shuffled to stand next to them and gave them a critical look over before sighing. He reached out and carefully repositioned Katsuki so that he was sitting on the ground next to Izuku instead of pinning him to the ground. As soon as the spell lifted, Katsuki vanished Ground Zero and sat cross-legged, scowling at the ground.
Izuku, on the other hand surged forward, apology on his tongue. "Yagi-sensei, I-"
"I'm so sorry." Izuku bit his tongue and furrowed his brow in confusion before he realized that for once he wasn't the focus of Yagi's gaze. "Young Bakugo, I have failed you most egregiously, and I will never stop apologizing for that." Katsuki said nothing, but Izuku was intimately familiar with the way his shoulders tensed and started their slow creep up towards his ears. "I should have noticed before. I-"
"It's too late." Izuku's gaze snapped up again, his breath stuck in his throat. Katsuki's voice was low and gravelly, but it lacked nearly every bit of heart it normally held. Instead it sounded shredded, like every word was sheer agony to say, physically and emotionally. He got to his feet, and nobody mentioned the slight tremor in his hand. "Why did you pick Deku? Why him of all people?" he demanded. "It had to have happened when that giant Heartless attacked. Did you pick him because I was too weak to defeat it? Because I lost?"
"Young Bakugo, I picked Midoriya because you were strong ." Katsuki's eyes widened for a moment before he screwed them shut and glared down at his fists. "I know you fear the Light in Midoriya's heart, and this new found power he wields, but you have it within yourself as well. The two of you burn equally bright, like twin stars on a pitch black night."
Katsuki snorted derisively. "If I have so much damn Light in my heart, how was it so easy for Shigaraki to do whatever it is he did to me? If I'm so strong, how do I give into Darkness so easily?" He balled his fists at his sides and squeezed his eyes shut again. "If I have so much power, why can't I beat this ?"
The next sound Katsuki made was a soft puff of the air getting knocked out of his lungs and Yagi pulled him into a tight hug. "All of that isn't in spite of your power, it's because of it. The closer you get to the Light, the longer and darker your shadow becomes. Alone, you have faced this challenge, and you have yet to fall. You have the strength of many within you, Young Bakugo. Remember that."
Katsuki made an almost imperceptible pained sound before he pulled himself out of Yagi's hold. He turned his attention back to Izuku, who was still on the ground, staring up at him. "Get the fuck up, Deku," he snarled. Izuku clambered to his feet, and he could have sworn he saw Katsjki's hand twitch towards him before it was harshly reeled back into place. "You think you're ever going to beat me sitting on the damn ground? Get real."
"Right!"
"Tch."
Yagi chuckled softly at their antics, bringing him back to the center of their focus. "The two of you are going to do great things," he said as he led them away. "One day you may do even greater things together. But until then, see each other as a goal. Something to strive for. Better yourselves to best one another. Today, the two of you are proper rivals."
Izuku's heart thumped in his chest at a million miles an hour, and he looked over at Katsuki. As usual, he had his head tilted up to stare down at Izuku with a furrowed brow, but instead of anger in those red eyes, they investigated him. Izuku was being looked over, measured up, and he desperately wanted to know where he fell. "Kacchan?"
Katsuki snorted again and looked away. "Fine, we'll be rivals. Doesn't matter, I'm going to win anyway."
Izuku grinned and he clenched his fists in excitement. "Well, then I'll get even better until I can beat you!"
"I'll always surpass you, stupid Deku!"
"Then I'll go even higher than that!"
"You idiot, you're not listening! I said I'm gonna beat you in every way!"
Izuku continued arguing with Katsuki, determined to keep pace at his side as Katsuki started walking back towards the dorms, but he paid close attention to Yagi. He was following along with them, a few steps away to give them some semblance of privacy with a small, secretive smile on his face. But as they approached the front door of the dorm, Izuku noticed that smile fade, replaced with a concerned downward tilt. Katsuki didn't seem to pay it any mind, but Izuku heard Yagi's words echo in his mind and his heart, as loudly as if they had been spoken directly in his ear. He turned to ask Yagi to explain, but the old Master was already walking away.
May your hearts be your guiding key.