In the ninja world, the strong were revered. That was the only law.
Momochi Zabuza, within the range of Uchiha Yue's Purple Eye, was an elite of Kirigakure's new generation, even in the village known as the "Bloody Mist." Otherwise, how could a ninja of Zabuza's caliber have been sent to train at the Land of Water's second line of defense and join the Kirigakure forces guarding it?
Yet Momochi Zabuza, who had only just begun to make a name for himself in the Shinobi World, had terribly bad luck. Just as he joined the Kirigakure ninja forces stationed at the Land of Water's second line of defense, Uchiha Yue led the Uchiha Clan's elite in an assault on that very defensive line.
More tragically, Zabuza, who had yet to possess the strength of a jonin, ran headlong into Uchiha Yue on the battlefield. They might have been about the same age, but Yue was far stronger than Zabuza. In the midst of his frenzied slaughter, Yue might not even have realized that he had defeated Momochi Zabuza, a future member of the Seven Ninja Swordsmen of the Mist.
After that defeat at Yue's hands, Zabuza was left with a shadow over his heart. Whenever someone mentioned Uchiha Yue's name, he could not suppress the fear within him. At times, merely hearing Yue's name could drive Zabuza mad. Yue had inflicted endless nightmares upon him on that battlefield, leaving Zabuza—who had once believed he could dominate the Shinobi World—utterly devoid of confidence.
That was right. The current Momochi Zabuza was a Momochi Zabuza without a shred of confidence.
After barely escaping Yue's grasp during the fighting at the Land of Water's border, Zabuza, whose body was almost entirely covered in wounds, fled miserably into the Land of Water and began