This was the stable boundary passage—a specially reinforced corridor within the Dangai (Precipice World).
Unlike the main Senkaimon that connected Soul Society and the Human World, this was a controlled subspace, engineered and maintained by the Shinigami Research and Development Institute for long-term spatial experimentation.
Kurotsuki Renya stood before the massive structure alongside Soi Fon and Nemu Kurotsuchi.
The gate before them was not made of wood or stone but reinforced spiritual alloy, etched with Kidō circuits and rotating time-stabilization glyphs. A large chronometric dial was embedded at its center, constantly measuring temporal distortion.
"This is the stabilized transmission gate," Nemu explained calmly. "It allows entry into a fixed sector of the Dangai without triggering spatial collapse."
The door slowly opened.
The moment they stepped inside, the air changed.
Inside the Dangai
They emerged into a vast, suspended space—an artificial pocket carved out of the turbulent boundary between worlds.
Eight silver restraint pylons were embedded around the perimeter, four on each side, suspended in the void itself. Spiritual conduits connected them to a central platform.
At the center stood a reinforced spiritual chair, designed specifically for captain-class reiatsu circulation.
Renji Abarai was already seated in it, breathing heavily.
Nemu stood beside him, calmly monitoring several instruments.
"Renji?" Renya asked, slightly surprised.
Renji grinned weakly. "Heard you were coming to train here. Captain Kurotsuchi ordered me to assist with the calibration."
Renya nodded. "So you're the test subject."
"Tch. Lucky me."
Mayuri Kurotsuchi's distorted voice echoed through the chamber.
"Enough chatter. This isn't a social gathering."
He gestured toward the surrounding devices.
"These restraint pylons regulate the Dangai current. Without them, time compression would crush the subject instantly. The chair channels spiritual pressure into the stabilizers, preventing the Kōtotsu from detecting your presence."
Renya studied the structure carefully.
"And the Kōtotsu?" he asked. "If it passes through?"
Mayuri let out a dry chuckle.
"Then it will be redirected."
He pointed to the black, stake-like constructs embedded along the outer ring.
"These are displacement anchors. When the Kōtotsu approaches, its trajectory is forcibly diverted into an adjacent temporal layer."
Renya's eyes narrowed. "You can reroute the Kōtotsu itself?"
"Of course," Mayuri replied smugly. "The Dangai is nothing more than layered space-time. Once you understand the rules, it becomes… adjustable."
Renya exhaled slowly.
If this system held, it meant continuous training inside the Dangai—something previously thought impossible.
Mayuri continued, "This environment allows extreme time dilation. One day outside equals nearly forty days within. However, the system requires constant reiatsu supply."
He glanced at Renji. "Which is why your captain is currently acting as a living stabilizer."
Renji groaned. "I can hear you, you know…"
Renya stepped forward. "What about prolonged use? Can this system remain active indefinitely?"
"Only if the reiatsu supply remains uninterrupted," Mayuri replied. "Food rations have been compressed and placed nearby. Nemu will remain here to oversee operations and maintenance."
Nemu gave a small bow. "I will remain until the training concludes."
Renya nodded in understanding.
"And after the session?" he asked.
"The system will be dismantled," Mayuri said. "If left unattended, the Dangai will consume it."
Renya turned toward Renji. "Then recover your strength. I'll begin shortly."
Renji smirked. "Don't overdo it, Captain. This place isn't forgiving."
Renya stepped forward, taking his place at the center of the chamber.
As he settled into position, the spiritual pressure around him began to rise.
The space trembled.
The Dangai responded.
This was not ordinary training.
This was forced evolution.
And Renya intended to survive it.