After using his new power to punch Haku while dispelling his mirrors, Naruto regains control of himself when Haku's mask breaks away, recognising him as the boy he previously conversed with. Asking Naruto to kill him as he had failed Zabuza, a flashback reveals that he had inherited his ability from his mother.
It is then shown that he once lived in the Land of Water, where people with Bloodline Limits were forced to conceal their powers out of fear of persecution. When Haku's father learned of his power, he killed Haku's mother, forcing Haku to subconsciously invoke his powers to kill his father and the angry mob.
Some time after, Haku was found by Zabuza and trained to hone his skills to be of use to the swordsman. Meanwhile, having sensed Naruto only released a fraction of the Nine-Tails's chakra, Kakashi summons a number of dogs to find and restrain Zabuza.
Zabuza glanced at Aika who had her eyes closed. At that time, Haku manages to convince Naruto to kill him before seeing Kakashi about to finish Zabuza off with his Lightning Blade Technique.