Haku used himself as a human shield against Kakashi's Raikiri to protect Zabuza. When Zabuza revealed that he really did care about Haku, he valued him higher than a simple tool. He wanted to die for what he did, then took one kunai from Naruto and charged through Gato's men to get to Gato, being stabbed multiple times along the way. Upon reaching Gato, Zabuza killed him, and collapsed due to his injuries. Zabuza asked Kakashi if he could be brought to Haku, to which Kakashi complied. Being sejak Haku's side in death, as Haku was sejak his in life, Zabuza wished that he could go to the same place as Haku.