Collapse and Fusion
The fortress began to scream. That was the only way Ruko could describe it as the walls trembled and distant shockwaves rolled through the hidden chamber. The air shifted violently, dust and fragments shaking loose from the ceiling as the battle elsewhere reached its peak. He could feel it now—the adventurers scattering, magic colliding, the unstable rhythm of a structure being pushed beyond its limits. Somewhere not far from here, Kazuma and the others had reached a critical point. Then Megumin cast Explosion.
"Wait... what is that noise." Even from deep within the true core chamber, the blast arrived like a god striking metal. The impact tore through layers of reinforced structure, the shockwave ripping down the rune-lined corridor and slamming into Ruko's body before he could brace. "What the bombo—" The floor cracked beneath him. The pedestal fractured. He stumbled. It wasn't graceful. It wasn't heroic. His boot slipped on debris, balance lost for half a second too long, and he fell forward directly into the pedestal holding the third Sha-Obelisk fragment. Contact.
The moment his hand brushed the fragment, something inside him responded instantly. The two fragments already within him ignited in resonance, a violent synchronization that felt like his bones were ringing. "W-What the... their fusing?" The third fragment shattered into light and drove itself into his chest without resistance, not piercing flesh but phasing into him as if he had always been incomplete. "And its gone right inside. Wait why does it sound sus!" Pain detonated through his entire body. Not surface pain. Not muscle or skin. It felt like his nervous system was being rewritten.
Ruko gasped, but no sound came out. His vision whitened. The fragments fused within him in a surge of energy so dense his thoughts fractured. He could feel the alignment happening—three becoming one—structures interlocking, stabilizing, expanding. Then the Eternal Thread reacted. "Oh my god. Why is it your turn!" The coiled strands snapped to life and launched forward, wrapping around him in an instant. They moved with intention, weaving around his torso, arms, and legs in tight spirals. They avoided his face, leaving his vision clear, but everything else was bound in luminous filament that pulsed with raw mana.
Oh oh what is this. I feel like i got myself something new to impre—" And then the real agony began. It wasn't just physical. It invaded his mind. "P-Please don't tell me there's a side effects!!" Every thought splintered into noise as the Thread forced synchronization between his body and the mana now flowing through him. It wasn't gentle. It wasn't patient. It was correction. "It's feels like my body is tearing apart AAAAHHHHHH!!!" His knees hit the floor. For ten seconds, he was nowhere.
The pain was so absolute that his brain tried to shut itself down. Every instinct screamed to pass out, to escape, to retreat into unconsciousness. But something inside him refused. Not pride. Not stubbornness. Just a refusal to disappear. Ten seconds felt like drowning in light. "What is this place of... nothingness?" He couldn't hear the collapsing fortress. He couldn't feel the ground. He couldn't even remember his own name. And then—Silence. The pain stopped as abruptly as it had started.
Ruko remained on his knees, breathing ragged, sweat dripping from his jaw. The Eternal Thread loosened slightly but did not detach. Instead, it settled against his body like a second skin, faintly glowing, integrated. His mind cleared. "Gasp! Kuff-kuff... kuff-kuff! Lucky thing I survive somehow." And for the first time, he could feel it fully. Mana. Not as distant hum. Not as ambient pressure. Not as something external. It flowed through him. Not violently. Not overwhelmingly. Naturally.
He could sense currents in the walls, the instability of the collapsing systems, the residual energy from Megumin's Explosion radiating outward. He understood pathways without seeing them. He understood pressure points without analyzing them.
Yew: [Host has Mana Flow. Unlocked.]
He ignore her since he didn't need instructions. He didn't need someone to explain it. It was like discovering he had been walking blind his whole life and had just opened his eyes. His gloves—Lumy's Core Alloy—cracked along the seams. "Huh?" Her core peeled away from his hands and condensed into a single red stone that dropped to the floor for half a second before leaping back up and embedding itself into his palm. It fused there without blood, without resistance, pulsing once as if confirming reintegration.
"Hmph! i guess... you don't want to leave me too... lumy." Ruko slowly pushed himself to his feet. The true core chamber was collapsing now, cracks racing along the walls. The Eternal Thread retracted fully into his body, no longer visible but undeniably present. The fragments within him were stable, unified. Somewhere deeper in the fortress, a surge of unstable mana spiked violently. "Wait this strange mana. Kazuma!" Ruko moved. Not clumsy. Not rushing. Precise.
He navigated the collapsing corridor with unnatural clarity, stepping around falling debris before it landed, shifting through unstable passageways as if the structure's intentions were transparent. He didn't question it. He simply moved. When he emerged into a larger chamber, he saw them. Kazuma was gripping part of the core system, face strained as he used Drain Touch to siphon overwhelming mana. Wiz stood nearby, chanting through visible exhaustion, preparing teleportation magic far beyond safe limits.
They weren't trying to destroy it. They were redirecting it. "If we let it explode here, Axel's done for!" Kazuma shouted through clenched teeth. Wiz nodded weakly. "We will try send it… somewhere empty… or far enough…" Ruko knew where but don't want to admit it. A noble's land. Consequences would follow. They always did. The fortress's energy peaked violently as Wiz completed the teleportation sequence. Mana warped around the core, compressing, distorting, then vanishing in a blinding flash that tore the pressure out of the chamber in one violent vacuum pulse. Silence followed.
The structure around them began its final collapse, now empty of power. Ruko stood there, breathing steady, watching as Kazuma nearly collapsed from mana drain and Wiz struggled to remain upright. No one looked at him. No one noticed what had changed. He glanced down at his hand where the red stone rested in his palm, warm and quiet. No explanations. No announcements. Just only a aftermath.