Mui

was the primary antagonist that appears in Naruto 5: Blood Prison. He was the of the prison castle Hōzukijō and a jōnin-level shinobi from Kusagakure.

Background
Mui's wife passed away not long after their son, Muku, was born, so he raised him all by himself. He was a caring father who loved his son deeply, often taking Muku to eat ramen. Ten years ago, as the guardian of the Box of Ultimate Bliss, Mui, tried opening it once with Muku's chakra, in the hopes of asking the box to grant them the wish of reviving Kusagakure to its former glory. However, Muku didn't have enough chakra and was sucked into the box instead, leaving Mui grief-stricken. As a result, he sought a way to reopen the box to ask for his son back, unbeknownst to his superiors.

Appearance
Mui had long black hair that goes beyond his shoulders. He wore some sort of suit with a brown belt and a silver buckle. He also wore goldish-brown boots.

Abilities
Mui had shown great skill with taijutsu, able to defeat multiple prisoners barehanded without losing his composure, as well as easily defeat a weakened Naruto with a series of swift punches. Even after suffering a mortal wound through his chest by his son, Mui managed to get back up on his feet and apply a powerful seal. Mui also has knowledge of pressure points, knocking Naruto unconscious with few strikes.

Nature Transformation
Mui had demonstrated great proficiency with Fire Release. The most prominent of his fire techniques was one which can bind a prisoner and prevent them from moulding chakra while at the same time absorbs their chakra after he applies a formula to them, it will also set them aflame should they try to escape. He also had an advanced form of this which he can use on larger targets. By altering this technique, he can surround his arm with fire to use as a blade which can use to engulf those he stabbed in fire.

Trivia

 * His name means "inactivity".