Mui

Mui is stern, distant, and apparently indifferent to questions of guilt or innocence, insisting that his duty is to contain prisoners sent to him by the hidden villages.

His emotional restraint conceals a consuming attachment to his son. That unresolved loss drives decisions that conflict sharply with the discipline and authority he projects as prison master.

Mui's signature technique is Fire Release: Heavenly Prison, a seal placed directly onto a target's body. Attempting to mold large quantities of chakra causes the seal to heat violently, allowing Mui to suppress prisoners with minimal guards.

He is also capable of summoning Hōzuki Castle's ninken and possesses the combat ability expected of a Kusagakure jōnin.

Mui brands Naruto Uzumaki with Heavenly Prison when Naruto is sent to Hōzuki Castle under accusations of attacking major shinobi leaders.

Mui's true objective is to use Naruto's enormous chakra to open the Box of Ultimate Bliss and recover his son Muku, whom he lost to the box years earlier. The resurrected Muku emerges corrupted as Satori and fatally wounds Mui. Mui later helps Naruto create an opening to defeat him.

Muku is Mui's son and the driving force behind his actions. Mui originally sacrifices him in an attempt to open the Box of Ultimate Bliss, then spends years trying to undo that decision.

Ryuuzetsu was Muku's childhood friend and opposes Mui's effort to reopen the box. Naruto Uzumaki becomes the source of chakra Mui needs, while Maroi infiltrates the prison amid the larger conspiracy.