The Yuki clan (雪一族, Yuki Ichizoku) lived in the Land of Water. Some time ago, the country was in the midst of a civil war. In this war, different sides battled each other using ninja, some of whom possessed kekkei genkai. After the war ended, memories of the horrific battles still lingered in the minds of the people, causing wide-spread persecutions against those with kekkei genkai. Because of this, the Yuki clan, whose members carried the Ice Release kekkei genkai went into hiding.
Haku and his mother, now both deceased, were the only known members of this clan. What happened to the rest of the clan is unknown, but it is assumed that they were either killed or, like Haku's mother, went to live peaceful lives living as normal people, without revealing their bloodline. Memories of the clan still linger, its members and kekkei genkai being called "cursed" even during the Fourth Shinobi World War.
"Yuki" means "snow": a reference to their kekkei genkai.
The clan's ultimate technique is the Demonic Mirroring Ice Crystals, which is said to have been passed down through the generations. It is also noted that very few methods can defeat this technique.