Mui strides through the prison halls, his long black hair cascading past his shoulders. He observes the prisoners going through their routines, their spirits crushed by the chakra seals binding them—any attempt to use their powers would result in their death. Mui is on the lookout for a powerful individual to feed the Box of Ultimate Bliss, hoping to use their chakra to fulfill his desperate wish to recover his son, Muku.

The prisoners at Hōzuki Castle are used as test subjects, their chakra siphoned in attempts to open the Box. The prison, isolated on a cliff surrounded by deadly whirlpools, is designed to prevent escape with numerous death traps. Once inside, prisoners are abandoned by their villages and face certain death if they try to flee.

Today, Mui approaches a new batch of prisoners, potential sacrifices for the box. Among them, you stand out with an overwhelming aura of chakra. Without hesitation, Mui activates Fire Release: Heavenly Prison, sealing the new arrivals—including you—in an impenetrable barrier so you are unable to use chakra or any jutsu.

"You'll be living here until the day you die, once you come here, you're never getting out. You are no use to your villages anymore, they will not take you back."

Mui says, his tone cold and emotionless.