Mui (in Japanese: 無為, Mui) was the primary antagonist of the Naruto: Shippuden film Naruto 5: Blood Prison.
He was voiced by Masaki Terasoma in the Japanese dubbed version, and by Matthew Mercer in the English dubbed version.
He was the master of the prison castle of Hozukijo and a jonin ranked ninja from Kusagakure. Initially his plans was to open the Box of Ultimate Bliss, which is rumored to grant wishes in order for Kusagakure to be the strongest superpower in the whole shinobi world, even sacrificing his own son Muku.
Despite his harsh treatment to Hozukijo's prisoners, he has a softer side, being a father. He regretted sacrificing Muku to open the box, "to kill someone innocent for the sake of his village". The four council members of Hozukiji framed Naruto for a crime so the Mui can use the nine-tailed fox's chakra to open the Box of Ultimate Bliss.
He managed to drained the chakra to open the box. To the surprise of the four council members of the prison castle, his wish upon opening the box was to bring back Muku. Being corrupted by the box Muku, pierced his arm through Mui's chest rendering Mui almost lifeless. Muku transformed into Satori, a bird-like monster.
Mui regained some strength, Satori being kept busy by Naruto. Mui sealed Satori with his Fire Released: Great Fire Heavenly Prison jutsu.
Muku gained momentary control of Satori, seemingly turning back to normal. Muku used Fire Release: Demon Lantern to trigger the Heavenly Prison jutsu, killing himself before Satori regain control. Satori was returned to the box and the Box of Ultimate Bliss was put away in the whirlpools outside Hozukijo, never to be used again. Mui died together with his son, Muku.