"Forty minutes on the dot, Boss. Time to wake up."
The soft, melodic voice of Seraphina drifted into Shin'ya's consciousness, dragging him out of the abyss of his forced sleep loop. He blinked open his eyes, wiping a stray piece of moss from his cheek, to see Sera kneeling beside him. In her petite hand, she was holding a delicate, silver pocket watch, its second hand ticking precisely.
Shin'ya sat up abruptly, his eyes wide as he looked from the pocket watch to her face. A wave of profound, existential gratitude washed over him. Without a reliable anchor, his body's unique curse could have trapped him in a chain of endless naps in the middle of a monster-infested forest.
He grabbed Sera by the shoulders, his expression deadpan but his eyes screaming with intense, chaotic energy.
"Sera," Shin'ya said, his voice trembling with deep emotion. "You are an absolute saint. An angel sent from the heavens. Tell me what you want. Do you want gold? Do you want a mansion? Do you want every single bit of my guild earnings from this S-rank mission? Just say the word and I will sign over my entire life savings to you right now."
Sera's face instantly flushed a violent shade of pink, her hands flailing wildly as she tried to pull away from his intense grip. "S-Shin! Please! I was just doing my job as your liaison! I don't need your life savings! Please don't give me your money!"
"Are you sure?!" Shin'ya pressed, completely serious. "Because forty minutes exactly is a mathematical miracle!"
"I am sure! Please sit down!" she cried out, laughing nervously.
Shin'ya slowly let go, letting out a heavy breath as he slumped back onto his knees. The comedic relief quickly faded as his eyes drifted back toward the northern horizon, where the catacombs lay buried deep beneath the earth. He clutched his chest, feeling his heart still hammering against his ribs from the sheer exhaustion of his previous training.
"This is bad," Shin'ya muttered, rubbing his temples. "My silent landings are getting better, but my stamina is an absolute joke. Every time I use Shadow Slip, I lose my breath. The shadow dimension has zero oxygen. If my physical endurance stays like this, I will suffocate and pass out before I can even get close to the Grave-Weaver Titan to drill that holy spike in."
He groaned, staring at the sky. "How the heck do normal people even build up lung capacity? I didn't exactly read fitness manuals in my past life."
Sera tilted her head, trying to be helpful. "Well... the elite scouts of the Oakhaven military practice running up steep hills while wearing heavy iron vests to force their lungs to expand."
Running while restricting oxygen...
Shin'ya's anime-nerd brain instantly clicked. Wait. That's just real-world hypoxic sprint training! Free-divers and Olympic athletes do that to build CO2 tolerance!
Shin'ya stood up, a terrifyingly determined glint in his eyes. "Alright. If reality won't give me a cheat code, I'll just have to break my own lungs."
"Um... Shin? What are you doing?" Sera asked, taking a cautious step back.
"I am inventing a new training methodology," Shin'ya declared dramatically. "I call it... The Suffocation Sprint."
Without giving her a chance to question his sanity, Shin'ya took a massive, deep breath, filling his lungs to maximum capacity. He immediately dove into the darkness.
Shadow Slip
He moved like a silent bullet through the shadows of the forest floor. Five seconds... ten seconds... fifteen seconds. The familiar, suffocating pressure built up in his chest. His lungs screamed for oxygen.
The moment he couldn't take it anymore, he popped out of a tree's shadow into the real world—but instead of breathing, he forbade himself from inhaling, Keeping his mouth tightly shut, he forced his burning, exhausted legs to sprint at absolute maximum speed across the clearing.
His vision blurred. His heart pounded like a war drum. His brain was actively flashing red sirens. It was pure, unadulterated psychological and physical torture.
Just Three More St-steps! he screamed internally.
Finally, his legs gave out and he tumbled into the grass, gasping for air so violently he thought his ribs might crack. He inhaled the crisp forest air like it was the finest delicacy on earth.
"SHIN?!" Sera shrieked, sprinting over to him with a canteen of water. "Are you trying to kill yourself?!"
"N-No..." Shin'ya wheezed, a delirious, triumphant smirk spreading across his sweaty face. "It's... working."
For the next several hours, the peaceful forest clearing became a stage of absolute madness. Shin'ya subjected himself to the brutal cycle over and over again. Dive into the shadow, suffocate, pop out, sprint while still suffocating, collapse, breathe, repeat.
It was a primitive, hyper-aggressive form of training, but his fourteen-year-old body, fueled by the pure magic of his Shadow affinity binded Ketsugai, was adapting at an unnatural pace. His heart was learning to pump blood efficiently with less oxygen. His lungs were expanding.
As the sun began to dip below the horizon, painting the sky in shades of deep orange and purple, Shin'ya prepared for his final test of the day.
He took a breath. He dropped into the shadow.
He moved forward. He hit his usual fifteen-second limit where his lungs normally felt like they were going to explode. But this time, he pushed past it.
One Second....
Two Second....
He traveled an extra fifteen feet entirely within the safety of the dark before finally surfacing. He landed with a soft, nearly imperceptible puff on the grass, taking a controlled, steady breath.
He had extended his shadow-hold by exactly Two Seconds.
It sounded small. It sounded insignificant. But to an assassin operating in an S-rank, soundless death zone, those two seconds meant he could cover a massive distance without ever revealing his physical body to the stalkers or the sleeping titan.
Shin'ya looked down at his trembling, sweat-soaked hands, a genuine smile breaking through his deadpan mask.
"Two seconds," Shin'ya whispered, his voice full of resolve. "I can work with this."