The Blood Crystal Sentinel
The rear wall of the Blood Crystal Martial Artist failure storage room looked at first like ordinary warehouse paneling, but up close one metal panel in the middle was noticeably less rusted than the rest. Yu-jin shone her flashlight on it, revealing a hairline seam. Ha Yul placed her hand against the section. There was no lock on the other side. It had simply been built to look like it might not be a door at all. When it opened, a staircase leading downward appeared.
Yu-jin paused at the top of the stairs and peered into the dark. The darkness below was thick, almost as if it were swallowing light, and from somewhere deeper came the intermittent, brief whine of machinery. “From here on, we’re in territory that’s been completely erased from the maps. Even after confirming the failure storage room, there’s still more below. That means someone either designed this entire place in stages from the beginning, or they found the bones of an old city and overlaid their own purpose on top of it. Either way, these aren’t ordinary people.”
Ha Yul descended first. She kept her footsteps as quiet as possible, yet the old steel stairs announced their presence with every tiny vibration. At the bottom stretched a long corridor. The ceiling was low, only half the lights still worked, and the floor bore clear tracks from heavy loads being moved repeatedly. Wheel marks mixed with shoe prints and footsteps spaced at regular intervals. Ha Yul crouched to examine them. The weight distribution was consistent, the stride never wavered, and even the turns showed minimal deviation. It was difficult for a conscious human to walk that way. A trained martial artist could manage it, but that only made it stranger. Movements this standardized felt less than human.
At the end of the corridor they found a wide underground level that looked like a cross between an abandoned military command center and a laboratory. In the center was a large empty space, surrounded by glass-walled isolation rooms, observation stations, data terminals, and red warning lights. Several wall screens still emitted faint afterglows, displaying fragments of body-response graphs, Blood Qi amplification values, pain-suppression rates, and command-execution success rates. Ha Yul read the labels slowly. They quantified how little pain the test subjects felt, how strongly their Blood Qi was amplified, and how obediently they followed orders. Failures at least broke down. The metrics here assumed subjects who still retained human form while having their will to resist as humans cleanly removed. They were combat test subjects.
At that moment, footsteps echoed from ahead. A single person’s footsteps. Neither heavy nor light, but excessively controlled. Ha Yul and Yu-jin looked up at the same time. Someone was walking out from between the half-open fire doors on the far side of the empty central space. At first glance Ha Yul thought it was a martial artist. Tall, broad-shouldered, still maintaining human shape. But as the figure drew closer, she saw it: the back of the neck, near the cervical vertebrae. A red Blood Crystal embedded there glowed dully beneath the skin, and dark-red veins spread from it across the nape and down below the collarbone. The eyes focused like those of a normal person, yet held no human emotion.
The figure spoke. “Unauthorized intruder confirmed. Commencing intruder elimination protocol.” The voice was human. It neither cracked nor boiled like an animal’s. The pronunciation was clear. This was an existence modified to retain human-level intelligence while carrying out orders. Not a Blood Crystal entity, but a Blood Crystal Martial Artist.
Yu-jin rested her hand on her sword hilt. “Looks like the worst-case scenario came true. I figured there might be at least a guard or two, but I didn’t expect an actual success to still be here. Ha Yul, don’t treat that like an ordinary mutant. It’s a real martial artist. If the data on those screens is accurate, it doesn’t feel pain and its Blood Qi is probably amplified.”
Ha Yul had already drawn her karambit. She took a short breath while watching the opponent. “I know. It even smells different.”
The Blood Crystal Martial Artist did not wait for conversation. In the next instant its body slid forward across the floor. No wasted motion, no feints, only the shortest possible path. Ha Yul deflected the attack to the side and aimed her karambit at the wrist, but the Blood Crystal Martial Artist ignored the pain entirely and spun without breaking its movement, driving an elbow into her ribs. A dull impact traveled through her side.
Yu-jin’s sword immediately intervened. The blade, thinly coated in Blood Qi, thrust toward the Blood Crystal Martial Artist’s neck. Instead of retreating, the opponent stepped forward into the sword’s trajectory. It accepted the loss to close the distance. The blade cut into the space between shoulder and neck, yet the figure did not so much as frown and simply grabbed Yu-jin’s wrist to stop the strike. A human would have been delayed by pain; this one’s movement never faltered.
“Pain suppression is annoying!” Yu-jin gritted her teeth and twisted free. At the same time two gunshots rang out. Yu-jin’s bullets struck the Blood Crystal Martial Artist’s thigh and abdomen, but it only staggered and kept coming. The Blood Crystal at the back of its neck pulsed brighter, and Blood Qi surged throughout its body.
Instead of backing away, Ha Yul charged forward. Giving ground to an opponent like this would only let it claim the entire space. She tried to draw blood the way she did against monsters, but the opponent ignored the bleeding and continued moving. Its movements barely wavered. It fought like a human yet endured like a monster.
The Blood Crystal Martial Artist’s knee shot up like lightning and struck Ha Yul’s side again, exactly where she had been hit before. Ha Yul clenched her teeth and leaned back to lessen the impact. In that opening she drew her axe and swung upward in a wide arc. The blade bit deep into the opponent’s forearm, nearly severing it, yet the Blood Crystal Martial Artist, one arm now dangling, seized Ha Yul’s shoulder with its remaining hand and slammed her against the wall. Concrete cracked against her back. For a moment her vision went white.
Yu-jin immediately thrust her Blood-Qi-wrapped sword into the Blood Crystal Martial Artist’s side from the flank. The blade pierced through, and for the first time the opponent’s movement halted. Ha Yul did not miss the opening. She drew her hammer, forced down the blood rising in her throat, stepped in, and brought every ounce of strength down on the Blood Crystal Martial Artist’s knee. Bone shattered. At the same moment, Blood Qi exploded outward from the opponent’s body once more. Even with its knee half-bent, it did not fall.
“We have to break the Blood Crystal at the back of its neck!” Yu-jin shouted. The Blood Crystal Martial Artist changed direction and targeted her instead, as though prioritizing targets according to its orders. A First-Class Martial Artist that could use Blood Qi. It had apparently judged her the greater threat. Even dragging its broken leg, it closed in without losing much speed.
Yu-jin blocked with her sword, interrupted its flow with her pistol, and wrapped thin layers of Blood Qi around her body to boost strength and reaction speed. Yet the opponent was not fooled by feints that would have deceived a monster, nor did it stop for wounds that would have halted a martial artist.
Every time Ha Yul tried to breathe, it felt as though a hot blade twisted inside her ribs. Her ribs, and something deeper, were damaged. But she could not stay still. She could not leave Yu-jin to face it alone. More than anything, she could not die here. Chae-won and Su-min. The words they had shared at the café, the promise not to disappear without a word, the confession that had left them speechless, and the kiss that had followed. She had to return alive. If she wanted to avoid becoming someone who suddenly vanished beyond the reach of eyes, ears, and hands, she had to survive this place somehow.
She set the hammer down and took up the karambit and axe again in both hands. While Yu-jin held the opponent at bay with her sword, Ha Yul dropped low and slid beneath its guard, aiming for its back. The opponent read the movement, twisted, and drove its heel down. A heavy impact slammed into Ha Yul’s shoulder. Her body tilted, yet she used the forced-low posture to swing the axe upward. The blade tore deep into the muscle around the embedded Blood Crystal. Blood and red light sprayed outward. The crystal itself had not broken, but for the first time the opponent’s movements grew unstable.
Yu-jin did not miss the opening. She pushed more Blood Qi into her sword. The air around the blade trembled faintly as a membrane of Blood Qi formed along the edge. It was a technique that placed heavy strain on the body. Prolonged use would endanger even Yu-jin. Still, she had to use it now.
“Move!”
Ha Yul was already moving aside. At the same time she used her last strength to drive the karambit upward under the Blood Crystal Martial Artist’s jaw, forcing its head back. In that instant Yu-jin’s sword fell. The blade struck precisely at the back of the neck and crushed the cervical vertebrae where the Blood Crystal was embedded. The sound of the red crystal shattering rang out, an odd, compressed burst as though something long contained had finally exploded.
The Blood Crystal Martial Artist’s body convulsed violently. The veins that had spread along its dangling neck swelled for a moment before collapsing. It staggered backward several steps, still trying to maintain balance, as though determined to keep standing until its orders were fulfilled. But it was already too late. Without the Blood Crystal, its body lost its anchor and dropped to its knees. The upper body followed, and the head rolled to the side.
Silence fell. Ha Yul’s body, however, had no room to accept it. The moment the tension that had been holding her together snapped, pain she had been forcing down flooded in from her side, shoulder, arms, and back all at once. Simply drawing breath felt as though something inside her chest were tearing. Her knees buckled. The karambit slipped from her hand and clattered against the floor.
Yu-jin had been about to check the corpse again when she spun around. “You idiot! Why did you push yourself so far this time? You never fight like that, taking hits just to force your way in! You knew it wasn’t an ordinary monster, so why did you keep driving in with that body!?”
Yu-jin’s voice belonged to someone barely holding back anger, yet beneath it lay the terror of nearly losing Ha Yul. Ha Yul braced one hand against the wall and forced herself upright. The metallic taste rose in her mouth again, and speaking was difficult, but she managed, “……I have to go back alive.”
She had to return to Chae-won and Su-min. She had promised she would come back, that she would not disappear without a word. She could not end here in this basement. Ha Yul did not explain, but Yu-jin understood enough to feel even more twisted inside.
“……Damn it.”
Yu-jin spat the curse through clenched teeth. There was no time to be angry or sort through emotions. Since the Blood Crystal Martial Artist had been posted as a guard, the enemy would soon notice the signs of this fight unless they were complete fools. Escaping alive now took priority over searching deeper. Finding the next base would become much harder, but Ha Yul’s condition was more urgent.
Yu-jin pulled Ha Yul’s arm over her shoulder. The weight was heavy, the breathing shallow, and every small movement brought the sensation of blood pooling inside her side. Yu-jin assessed the injuries quickly. She had to keep Ha Yul conscious until they reached the surface.
“Don’t lose focus. Keep your eyes open until we’re up top. Breathe in short bursts. Deep breaths will hurt more.”
“……Understood.”
The two retraced their path upward. Yu-jin sent a short, rapid transmission to the Moorim Agency’s rear support. Priority change for on-site recovery, Kang Ha Yul critically injured, immediate evacuation requested, underground perimeter to be redeployed. Voices on the radio grew busy. Footsteps soon descended from above the stairs.
As they neared the surface, Ha Yul’s feet gave out once. Yu-jin caught her in something close to an embrace. The weight on her shoulder felt far heavier than usual. Ha Yul was strong. When hunting monsters she clung to her targets more tenaciously than anyone, refusing to let go until the end. Yet the fact that she could no longer even keep her own body upright struck Yu-jin as a harsher reality than the Blood Crystal Martial Artist they had just fought.
With the help of the subordinates who arrived, they reached the surface. Cold night air struck their faces. “No need to carry her. Straight to the car. Open the first-aid kit and prepare the oxygen tank. Just keep her conscious until we reach the hospital. And no one else goes below. Since there was a Blood Crystal Martial Artist posted as a guard, the enemy has likely already noticed whether they had people hiding down there or not. Forcing our way in will only get innocent people killed.”
The subordinates moved without argument. The car door opened and Ha Yul was half-lifted into the back seat. Yu-jin climbed in beside her. Every small jolt as the car moved struck Ha Yul’s body like a blow. She clenched her teeth and tried to steady her breathing while Yu-jin held her wrist and checked her pulse. Fast, but still holding.
Outside the window, Seoul still looked peaceful. Traffic lights changed, night buses passed, convenience-store lights glowed. Inside the car, however, one person was dying. Yu-jin spoke quietly, her voice lower and more pressed than before. “Keep holding on. Stay alive. Whoever you have to return to, whatever promise you made, I haven’t heard any of it yet, so explain it later yourself. If you pass out without explaining, I really won’t let it go.”
Ha Yul lacked the strength to answer with her eyes open, but she gave the smallest nod. There was a place she had to return to. People waiting for her. A promise that she would not disappear this time. That thought, that obsession, was the only thing still anchoring her fading consciousness.
The second exploration beneath Jongno ended that way. A lower level existed that selected successful specimens, and a Blood Crystal Martial Artist modified from a human had guarded its door. They had defeated it, but the cost was not light. And if the enemy was truly clever, they would already be concealing their next shadow through the breach they had created today. Even so, Kang Ha Yul was still alive. Because she had to return this time.