Warning! Article contains spoilers!
Also known as the Demon of the Hidden Mist, Zabuza Momochi is a missing-nin from the Hidden Mist Village and is the first main antagonist in the Naruto series.
Called the Demon of the Hidden Mist because of his childhood and him killing over 100 students when he was a child in order to become a Genin, Zabuza Momochi comes from the Hidden Mist Village [or Kirigakure]. Back when he was younger, the final test in order to become a Genin was to defeat everyone in your path, which meant killing them. Zabuza became a terrifying legend shortly after he killed so many, and he was enrolled into the ANBU after becoming Jounin. At the same time he was also offered a place in the group called the Seven Ninja Swordsmen of the Mist, because of his use of an extremely large sword constantly strapped to his back. Also in this swordsmen group was Kisame Hoshigaki, hence why links are always made between the two of them and their looks resemble each other.
Shortly after becoming part of both of those groups, Zabuza made an attempt to kill the Mizukage but failed, forcing him to run away. Because of this did he become a missing nin. He became listed in the Bingo Book, and during this time he met with a young boy with a curious kekkei genkai [bloodline limit] that allowed him to mix the elements of water and wind to form ice. This boy was none other than Haku, and Zabuza took him under his wing and trained him to become his 'perfect weapon.' When Team 7 defeated him and then he fought against his 'boss,' Haku risked his life for Zabuza and in return, Zabuza fought for Haku there after. In the end he asked Kakashi to bring him to Haku, where he whispered quietly to the dying boy, asking him whether he was crying at first, and then telling him that he was so sorry as the snow fell upon them and the pair died together. He is buried beside Haku just as they wanted it, and his sword is buried with them. Years later however, Sasuke Uchiha and Suigetsu Hozuki return to the grave and retrieve the sword for Suigetsu's use.
Zabuza appeared once again as one of the revived immortals from the Reanimation Technique by Kabuto. This was during the Fourth Great Ninja War. Kakashi with the help of other village's ninjas was finally able to trap Zabuza.
Zabuza was introduced to killing at a young age, hence why he has no problem attacking others. During his fight with Kakashi and the rest of Team 7 as they escorted a client back to the Land of the Waves, they crossed paths with him and his large sword, otherwise known as the Decapitating Carving Knife. The size and weight of the sword alone shows how powerful he is, not including the various water justus he uses such as Water Release: Grand Waterfall Technique and Water Release: Water Dragon Projectile Technique. He can also make water clones, a water prison which he used on Kakashi, and he can create mist.
Zabuza's signature technique is called the Silent Homicide Technique, or the Silent Killing Technique. Mist is formed around the battle field and Zabuza will come up noiselessly behind his opponent, killing them. This technique was attempted once during the fight between Zabuza and Kakashi, but Kakashi managed to get out of it and no one died.
 The Executioner
Zabuza's gigantic sword is known as The Executioner. In the case where it is broken, it will always be able to rebuild itself during contact with blood.
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