Haku

Haku is a ninja from the Land of Water. He has the ability to control two types of nature chakra (most can only control one):water and wind chakra. This gives him the ability to use ice chakra which is a mixture of the two. Haku's ability to use ice is his kekkei genkai, which is unnamed in the series.

The Land of Water was suffering from war, and ninja like Haku were hated. When Haku's father found out his wife has a kekkei genkai, he kills her, but before he could kill Haku, he was killed by Haku. Soon after, Haku met Zabuza and joined him as the rogue ninja's "weapon." In the Mission to the Land of Waves Arc, Haku appears as a Hunter-Ninja, giving the impression that he was sent to kill Zabuza (when he actually saved his life). He soon was revealed to be Zabuza's subordinate in the story and fought Sasuke and Naruto on the Great Naruto Bridge. Before Naruto could deal the finishing blow to Haku, he used the Body Flicker Technique to place himself in between Kakashi and his Lightning Edge and the trapped Zabuza, sacrificing himself for the one that mattered to him the most.

It is revealed that Haku and Zabuza met Kimimaro sometime while Zabuza was a part of the Hidden Mist Village.