The forest was colder than usual that morning, the wind sharp enough to sting skin through cloth. For Daigo, that wasn't a deterrent it was the perfect variable for his next experiment.
Oxygen deprivation had taught him what it felt like to be starved of the most essential resource a body could demand. Now, he wanted to teach his body to move between extremes, forcing it to function when battered by sudden, violent changes in temperature.
The idea came from battlefield memories: missions where shinobi fought in blazing deserts at noon and freezing rain at midnight, where fire jutsu filled the air with heat one second, and a snowstorm from another jutsu froze it the next.
Most shinobi adapted poorly to those swings. Daigo intended to turn them into his weapon.
For this, he returned to an abandoned lumber camp deep in the northern stretch of the forest. The camp had long since been swallowed by moss and vines, but it still held two useful assets:
A wide stone fire pit with a collapsed iron cauldron beside it.
A nearby stream fed by snowmelt, the water icy enough to burn on contact.
With a bit of work, the fire pit roared again, heat waves distorting the air above it. The stream ran just thirty meters away a perfect setup for quick transitions.
Daigo stripped to his training gear and stood near the fire until sweat began to run freely down his back. He wasn't just warming up; he was overheating.
Once his skin flushed and his heart rate ticked upward, he activated the First Gate. Blood surged faster, heat spreading through his body in waves.
Then the Second Gate. The heat multiplied instantly. It was like holding a sun under his ribs.
He began drills with a weighted staff, executing spinning strikes, low sweeps, and sharp thrusts. The fire's glow seemed to wrap around him, its breath clawing at his lungs.
By the time he reached the Third Gate, he could feel the sweat pouring into his eyes, his mouth dry like sand. Every inhale tasted like scorched air. His muscles moved faster, sharper but every second in the heat cost him more energy.
Without closing the Gates, he sprinted for the stream.
The first step into the water was like being stabbed in the shins. By the time he dropped to waist depth, it was worse each muscle locking up against the cold, skin screaming under the sudden loss of heat.
Daigo forced his breathing steady and submerged fully, letting the icy water crash over his overheated frame. His heart rebelled instantly, pounding in a confused rhythm, the Gates demanding blood flow while the cold forced everything to constrict.
Instead of tensing up, he began underwater combat movements: short jabs, slow kicks, and controlled rolls. The water turned his limbs sluggish, each motion echoing in his shoulders and hips.
He held the Third Gate for as long as he dared, the combination of heat shock and cold strain threatening to knock him unconscious.
Emerging from the stream, he didn't stop. He sprinted back to the fire, steam rolling off his body as he approached the blaze. The shock of sudden heat was worse than the first skin tingling, nerves confused.
Again he drilled his staff forms, then again into the icy stream.
He repeated this cycle five times.
By the fourth, his body was beginning to rebel in dangerous ways muscle fibers twitching uncontrollably, joints stiffening even as the Gates forced them loose. By the fifth, his vision blurred, and he could feel a deep ache building in his chest.
On the final trip to the fire pit, Daigo stumbled halfway there. His knees hit the dirt hard, the taste of iron in his mouth.
He had a choice: shut it down and live to train another day, or push through this wall and see what waited beyond it.
He chose the wall.
Opening the Fourth Gate was like tearing through his own ribs. The world lit up in red, the fire seeming dim by comparison to the heat inside him. He roared through a flurry of staff strikes, spinning so fast that the weapon blurred in the firelight.
When he finally collapsed, it was half-controlled, half-surrender.
Daigo lay on his back beside the fire, steam rolling off him into the cold air. His skin felt alternately frozen and scorched, muscles trembling under conflicting signals.
He closed the Gates slowly, forcing his body down from the edge. His breathing evened out, but his pulse still pounded like war drums.
By the time the sun reached its peak, the fire was just embers, and the stream still hissed faintly from where he had last stepped into it.
No one in Konoha would know. They would see him return looking as though he had simply gone on a long patrol, unaware that he had just forced his body to dance between two kinds of destruction.
As he dressed and prepared to leave, a dangerous thought stuck in his mind.What if he combined this with movement combat fighting in the fire's heat, then immediately fighting in ice water without pause? Not just drills, but against moving, striking opponents?
It would be reckless. Possibly lethal. Which made it exactly the kind of challenge he lived for.