Chapter 7: Core training! Core unstable

Rin awoke to the soft, filtered light of early morning. Her body ached all over, muscles sore from the previous day’s intense exertion. She winced slightly as she sat up, every movement reminding her of how far she had pushed herself. The flap of her tent shifted, and Shiro stepped inside with a small wooden tray. The steam rising from the bowls carried a comforting aroma. “Breakfast is ready,” he said firmly, setting it down before her. “You need all the energy you can get. Today won’t be any easier.” Rin rubbed her eyes, blinking blearily at him. “You’re really not giving me a break, huh?” she mumbled, half-smiling. Shiro crossed his arms, his expression somewhere between stern and amused. “Rest is for recovery. You’ve had that. Now… it’s time to learn how to stabilize what’s inside you before it tears you apart.” The words made her chest tighten. Rin glanced down at her hands, remembering the surges of uncontrollable energy, the way her body had nearly collapsed under its own power. Her “cores”—the truth she had only just begun to face—were both a gift and a curse. She picked up the bowl, forcing herself to eat even as her appetite waned under the weight of his words. Shiro’s gaze never left her, as if he was silently measuring her resolve. When she finished, he finally spoke again. “Good. After this, we start your core training. But Rin…” His eyes narrowed. “You need to understand something. If you keep treating your power like a bottomless well, it won’t just destroy you—it’ll destroy everything around you. Do you understand?” Rin swallowed hard, her throat suddenly dry.
“I… I understand.” Her eyes lingered on her untouched breakfast, the steam curling upward but doing nothing to ease the weight pressing against her chest. The fox’s words echoed in her mind, sharp and unrelenting. Shiro’s voice cut through her haze, calm but edged with curiosity. “Rin… tell me. What did your beast look like?” She hesitated, fingers curling against the table before she finally answered. “When I saw the fox… his color was a deep red. And his eyes…” She faltered, her own gaze dimming. “…they were the same as mine. I never saw his full body, only fragments.” Shiro leaned forward slightly, his tone sharpening. “Did you get his name?” Rin lifted her gaze toward him. “No, I—” Her words faltered as a sharp jolt ran through her. Her eyes flickered violently, shifting from their calm blue into a searing crimson, her pupils warping from soft circles into jagged, diamond-shaped slits. Both of Rin’s eyes flickered violently, colors snapping between blue and crimson until they settled into a blazing red. Her body pulsed with each rapid heartbeat, every thrum echoing like a war drum in her chest. A dark crimson aura bled out from her frame, twisting and shifting in jagged waves. Her nails elongated into sharp points, her gaze hardening as her eyes narrowed, razor-like in their focus. Rin staggered, forcing herself upright, her breaths ragged. “G-Get… away… sensei…” she growled through clenched teeth. But her voice warped, deepening, laced with venom. “You’re not putting me back into that damn cage!” the fox’s roar thundered through her throat, shaking the air. “Focus, Rin!” Shiro bellowed, his presence unwavering. Her body trembled violently, aura thrashing like a storm. Yet, through the chaos, her right eye flickered—returning to its calm, human blue. Gritting her teeth, Rin pressed her palms together, forcing herself into stillness. Even standing there, she began to meditate, trying to anchor her spirit against the beast clawing inside. Shiro’s eyes narrowed as he stepped closer, his hand hovering just inches from her shoulder, unsure if his touch would steady her or shatter her fragile hold. “Rin!” he barked, voice cutting through the chaos of the fox’s roar. Her aura flared violently, shadows and crimson light twisting like wildfire. “Sensei…” Rin’s voice cracked, half hers, half the beast’s. Shiro clenched his jaw, his fists trembling with frustration. He couldn’t drag the fox out from the outside, couldn’t chain it back down. All he could do… was reach her. “If you have to fight him—” Shiro’s voice thundered with urgency, his tone almost desperate, “—then fight with everything you’ve got! Don’t let him dictate your will. Make him bend to YOU!” Rin felt the water rushing past her ankles as she struggled to steady herself. Her eyes snapped open, blazing with fury. “Show yourself, YOU FRICKEN FOX!” she bellowed, fists clenching so tight the lightning around her arms sparked wildly. She looked up and saw it—the Beast Core, still trapped behind the same spiral. Determination surged through her. Without hesitation, Rin leapt toward the seal. A glowing mark formed across her stomach, pulsating with raw energy. All five fingertips of her left hand ignited, crackling with power as she pressed them firmly against the seal and twisted. The spiral shuddered, unlocking with a sharp click. But before she could react, the fox shattered the cage from within. A roaring blast of force hit her square in the chest, and Rin was sent flying backward, crashing into the water with a spray of waves, coughing and gasping for air. Rin staggered to her feet, her body trembling with raw power. She thrust her arm high into the air, arcs of lightning crackling and dancing along her skin like living fire. The energy coalesced in front of her, swirling violently into a massive, roaring sphere that pulsed with blinding intensity. “Thunderball of Destruction!” she roared, her voice carrying over the chaos, as bolts of electricity leapt from her body to feed the growing storm in her hands. Sparks hissed and crackled around her, the very air vibrating with the promise of annihilation. The fox snarled, its eyes narrowing as it watched Rin’s lightning sphere pulse with energy. Dark red aura began swirling around its body, coalescing into a massive, jagged ball of destructive force. Sparks of crimson energy crackled across its surface, arcs of power leaping outward like wild fire. “You think you can take me on?” the fox growled, its voice echoing through Rin’s very bones. The sphere hovered before it, rotating violently as if alive, emanating heat and pressure that warped the air around it. Bits of the ground and water nearby vaporized under the sheer intensity of its aura, sending waves of energy rippling toward Rin’s own Thunderball. The battlefield trembled, two immense forces building, poised to collide in a storm of lightning and raw power. Rin gritted her teeth, raising her Thunderball high. The fox mirrored her, its crimson sphere crackling with violent energy. “Now!” Rin shouted. Both spheres surged forward, lightning and crimson energy ripping through the air like twin storms. The moment they collided, the world seemed to shatter around them. A blinding flash erupted, illuminating the sky as arcs of electricity and jagged crimson energy danced and screamed across the battlefield. The water beneath them boiled and churned, waves erupting violently from the shockwaves. Air itself split with the sound of thunder and roaring power. Sparks flew in every direction. The two spheres twisted around each other, forcing energy outward, sending debris flying like meteors. Rin’s hair whipped around her face, lightning searing the air, while the fox’s aura lashed out like tendrils of molten fury. The collision hung for a heartbeat, both forces locked in a deadly stalemate—an explosion of raw, uncontrollable power threatening to rip everything apart. The spheres screamed against each other, lightning clashing with crimson fury. Rin’s arms shook violently, the Thunderball pulsating wildly in her grasp as the fox’s destructive sphere pressed back with relentless force. Her teeth clenched, muscles straining, sweat and sparks flying from her trembling body. I can’t let him win… she thought, feeling the raw pressure of the fox’s power trying to overwhelm her. Summoning every ounce of energy left in her, Rin pushed deeper into herself. Lightning surged through her veins like molten fire, arcs leaping from her body to feed the growing sphere. Her hair whipped around her face as her aura flared brighter, brighter, until the Thunderball glowed like a miniature sun, crackling violently as it expanded in response to her will. The fox’s sphere shook under her newfound force, sparks and fragments of energy exploding outward as the two colliding storms of power warped the very air between them. Rin gritted her teeth, pouring more and more of herself into the attack, refusing to yield. The fox’s crimson sphere wavered, the jagged energy flickering under Rin’s relentless surge. Its amber eyes widened, pupils narrowing in shock as it felt the raw force pressing against it. “Impossible…” the fox growled, its voice strained, reverberating through the storm. The aura surrounding its body flickered, unstable, as if the very energy that had once flowed effortlessly from it was now buckling under Rin’s sheer will. Rin’s Thunderball pulsed violently, arcs of lightning snapping outward like living tendrils, forcing the fox’s sphere to shudder and crack. The pressure of her power pressed deeper and deeper, and for the first time, the fox’s confident snarls faltered, replaced by a low, uneasy growl. The battlefield shook with the intensity, waves of energy radiating outward, as Rin’s determination forced the fox to reckon with the full might of her lightning. “IMPOSSIBLE! I’M ONE OF THE GREAT ANCIENT BEASTS! A MERE HUMAN CAN’T BEAT ME!?” the fox roared, crimson energy flaring violently as it poured every ounce of its power into the sphere. The two attacks clashed in a storm of light and sound, both forces straining against each other. Rin’s body trembled under the weight, every muscle screaming in protest. Crap… I can’t keep this up… she thought, vision blurring from exhaustion. “Shit…” Her arm gave out, collapsing beneath the unbearable strain. Her body pitched forward, crashing into the water as her Thunderball shattered with a deafening explosion, shards of energy scattering in all directions. The fox’s crimson sphere detonated at the same time, sending a shockwave that rippled across the water, waves erupting violently around her. Rin gasped, coughing, struggling to keep herself afloat, her body battered and trembling—but her eyes burned with stubborn defiance. The fox’s amber eyes lowered, fixing on Rin as she struggled to stay afloat, water dripping from her hair and clothes. “You’re not just some human…” he said, his voice low, almost thoughtful, yet still carrying that raw menace. He leaned slightly closer, the crimson aura around him flickering like a living flame. “The fact that you managed to push your lightning core past its limits… and keep going… is impressive,” he admitted, his tone a mix of respect. Rin’s chest heaved, her arms trembling, but a spark of determination flared in her eyes despite the exhaustion. “The name is… Karyu,” the fox rumbled, eyes gleaming with ancient fire. “One of the Ten Ancient Beasts.” Rin’s eyes widened, her chest heaving from both exertion and shock. Ten Ancient Beasts…? The words echoed in her mind like thunder. She could feel the weight of his power, even now, restrained in part by the cage—but the sheer presence of Karyu pressed against her like a living storm. “You… you’re real,” she whispered, almost to herself, her fingers trembling as she clenched them into fists. Karyu’s crimson gaze bore into her, unwavering. “Of course I’m real. And you… you are stronger than I expected. Most humans would have crumbled long before now.” Rin’s jaw tightened, her resolve hardening. “I’m not most humans,” she spat, a spark of lightning dancing across her arm as she straightened her posture. “And I won’t let you take control of me.” Karyu tilted his head, a slow, dangerous smile curling across his muzzle. “We shall see, little one… We shall see.” Rin’s body lay motionless in the water, every muscle screaming from the strain of the battle within. Hours passed, the world fading around her in a blur of exhaustion and pain. When she finally stirred, she awoke inside her tent, the soft morning light filtering through the fabric. Her body ached all over, and every breath felt heavy, but she was alive. Shiro knelt beside her, his expression a mix of concern and frustration. “Rin… you pushed yourself too hard,” he said, his hand hovering over her shoulder as if unsure whether to touch her. “You could’ve been seriously hurt.” Rin blinked slowly, trying to focus on him through the haze of exhaustion. “I… I had to,” she whispered, her voice barely audible. Shiro’s gaze softened slightly, though the edge of his sternness remained. “I know you want to master your core, but this isn’t just about willpower. You have to survive it. You have to control it, not let it control you.” Rin nodded weakly, the weight of the previous struggle settling over her. Shiro stayed there a moment longer, making sure she was steady, before finally standing. “Rest for now,” he said firmly. “We’ll start training again once your body can handle it. Understand?” Rin managed a faint nod, too exhausted to argue. Days passed in quiet recovery. Rin stayed in her tent, letting her body heal while Shiro monitored her progress. She spent the time meditating lightly, stretching her limbs, and focusing on controlling the residual energy of her beast core, careful not to push too far. The waterfall outside continued its steady roar, a constant reminder of the training yet to come. Each day, Rin grew a little stronger, a little more steady—her exhaustion slowly giving way to resilience. By the time the sun reached its peak on the third day, Rin’s body had regained its strength, her muscles no longer trembling at the slightest exertion. Her eyes, though still carrying the faint glow of her beast core, reflected a renewed determination. Shiro watched her quietly from the edge of the tent, nodding once. “Ready to continue?” he asked, his tone sharp but encouraging. Rin rose to her feet, fists clenched. “I’m ready,” she said, voice firm, steady, and filled with resolve. Only six months… six months until Shadow does what he’s planning… Rin thought, jaw tightening. I have to be strong enough to stop him… to control my beast core… to survive.