Mizuki

is a chūnin of Konohagakure and a former instructor at the Academy.

Background
As revealed in the anime, Mizuki was originally a childhood friend to Iruka Umino and stood up for him until he was overwhelmed by sheer jealous rage when Iruka was getting better treatment by everyone else. Despite his new-found hatred towards Iruka, Mizuki pretended to be his friend to be noticed and to discreetly keep Iruka miserable. Despite obtaining the rank of chūnin, being initially turned down from a position as an Academy instructor for being suspected of killing a team-mate on a previous mission, caused Mizuki to despise Konohagakure even though he eventually got the job. Orochimaru witnessed Mizuki killing his comrade in the aforementioned mission, and after praising him for taking such bold actions, gave him a specialised cursed seal. This meeting, coupled with feeling unappreciated due to initially being denied the position of Academy instructor, made Mizuki decide he would do whatever it took to rise to power and glory, even becoming a secret follower of Orochimaru.

Personality
Originally, Mizuki appeared to be very polite and kind-hearted, and was described to be a sweet man by his former lover, Tsubaki. In reality, he does not care for anything or anyone beyond his own rise in power. He takes pride in the fact that he is not bound by things like morals or teamwork, and is willing to sacrifice whatever he has to in order to complete his goals. His desire for power seems to come from what appears to be an inferiority complex, as he cannot stand having anyone look down on him. Mizuki's craving for power and acknowledgement led him to hate Iruka for gaining more attention than him, and pretended to be Iruka's friend in order to live off of that attention, as well as discreetly inflict misery on Iruka.

In what is perhaps an attempt to make him even more of an antithesis to Naruto, Mizuki's least favourite food is ramen, which happens to be Naruto's favourite. Mizuki also has a particular hatred for Naruto, seeing him only as the Nine-Tailed Demon Fox. It is unknown if Mizuki had started off with these negative traits and was merely hiding it with the façade of a sweet man, or was indeed once the sweet man Tsubaki claimed, but became corrupted as time passed. Mizuki is, overall, greatly ambitious and dishonourable.

Appearance
Mizuki has white shoulder-length hair with a slight hint of blue to it and green eyes. He wore the standard attire of the Konoha-nin before his defection, which included flak jacket and forehead protector that he wore like a bandanna. After his time in prison in the anime, he became much more muscular and well-defined in build to the point Naruto didn't recognise him at first. The clothing changed into an opened black vest, tight black pants, and a dark brown belt which had a silver rectangular belt buckle. His cursed seal which took the form of tiger-like stripes also gave him a more feral look.

Abilities
Originally, not much of Mizuki's skill was seen beyond proficiently wielding large shuriken. Later, in the anime, where he was revealed to have always been considered a very clever and talented ninja with a knack for learning advanced jutsu. In truth, the reason he had never advanced beyond chūnin was because there were suspicions on his conduct while in the field. He was also shown to be a very cunning manipulator from how he so easily deceived Naruto and then later the Legendary Stupid Brothers (although both cases were not too difficult, as Naruto was considered to be a little naive and emotionally desperate at the time, while the Legendary Stupid Brothers were simply immensely unintelligent).

After Mizuki's life in prison, his prowess increased considerably. He was strong enough to defeat a jōnin such as Shizune. He also had obtained an extreme amount of strength, able to almost easily overwhelm Iruka in their initial clash with a single hand. During his battle with Iruka, he demonstrated a new mastery of a random assortment of jutsu. While mostly improvised, he proved very capable of using them in creative combinations that Iruka just barely survived.

Animal Cursed Seal
Orochimaru has granted Mizuki a special tattoo which was a prescription of a potion that initially transformed him into a muscle-bound behaemoth of himself, with tremendous raw speed and strength. It also allowed him to gain the appearance of a tiger-like being with even greater strength but with much weaker speed, but since the potion was incomplete, his body was eventually destroyed, turning him into a shrivelled up old man. Although Tsunade managed to save his life and restore his body, Mizuki lost all of his battle and physical prowess and was never able to become a ninja again.

Prologue — Land of Waves
At the series' start, playing on the youth's desire to graduate, Mizuki duped Naruto Uzumaki into stealing Konoha's Scroll of Seals for him. Originally, Mizuki had the plan set up to have Naruto as a scapegoat and kill him to hide the truth of his deception and secretly leave the village with the scroll in his possession. However, Mizuki's plan is derailed when Iruka found Naruto first and decided to reveal Naruto's identity as the Nine-Tails's jinchūriki to ensure he runs off disillusioned. However, overhearing Iruka standing up for him, Naruto comes to his teacher's aid and uses the Multiple Shadow Clone Technique he had learned from the scroll to beat Mizuki unconscious for harming Iruka.

Mizuki Tracking Mission
In the manga, Mizuki claimed that he wanted the Scroll of Seals to gain infinite power for himself, and after his defeat, his fate remains unmentioned. However, the anime's filler arc showed that Mizuki intended to give the scroll to Orochimaru. Ending up at the Konoha Strict Correctional Facility after his defeat by Naruto, Mizuki bulked up by the time he stages a prison riot to escape from jail, intending to use the instructions given to him by Orochimaru to create a potion to increase his power and get his revenge on both Naruto and Iruka. Before that, he visited his lover, Tsubaki, who claimed that Mizuki used to be a sweet man, but that, ever since he got involved with Orochimaru, her relationship with Mizuki had faltered. Mizuki knocked out Tsubaki, whom he apparently did not love any more, and travelled to a cave where he could find the ingredients to the potion.

After consuming the potion, Mizuki obtained enhanced strength and power, stripes along his body, and enlarged arms. Later, as he added extract of a tiger into the potion, Mizuki assumed a tiger-like appearance but decreased his speed as Naruto managed to defeat him with the Rasengan. By that time, the flawed side effects of the Animal Curse Seal take effect with the defeated Mizuki reduced to a frail old man. Although his life was saved by Tsunade as she restored him to his original form, having no information on Orochimaru's whereabouts while being interrogated, Mizuki loses his ability to ninjutsu for what is later revealed to be have been a failed experiment of Orochimaru's.

Trivia

 * Mizuki's name means "cornel", a variety of the dogwood shrub.
 * According to the first databook:
 * His favourite food is chirashizushi while his least favourite food is ramen.
 * His favourite phrase is.
 * His dislike of ramen is likely a metaphor for his dislike of Naruto and Iruka.