You lie to avoid any injuries from fighting Haku and Zabuza

From Create Your Own Story

"Actually Zabuza also came. They both attacked me and jumped on top of a tree and killed themselves there to avoid anybody finding their bodies." Kakashi says "Oh. Glad that's over. Let's stay here for two more days then let's go back home."

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Two days later, when you are ready to go back home, Zabuza and Haku come and kill you all.