Yukina is a beautiful ice apparition whose tears turn into precious jewels. A filthy, human crime lord, Tarukane, once imprisoned her and made her cry the jewels. He hired two terrible brothers, the Torugo brothers, to make Yukina cry. He also imprisoned her by using these charms that hurt ice maidens when they're touched, and stuck them all over where Yukina was imprisoned. Kuwabara fell in love with her when he went to go save her with Yusuke and Botan. Everyone except Kuwabara and Keiko knows she is Hiei's sister.

After she is rescued, she returns home. Hiei never tells her that he is her brother. After she is saved by Yusuke and Kuwabara, she goes back home.

In the Dark Tournament, Yukina arrives in time to boost Kuwabara's morale enough for him to beat Risho and let the Urameshi team advance. She remains at the Dark Tournament, staying with the girls in their hotel room. She stays in the sidelines and doesn't play a particularly important role until after Yusuke beats Tuguro, and the stadium is collapsing. While standing at the top of the stands, a large chunk of concrete breaks from the stadium, ready to fall right on Yukina. Kuwabara moves to help her, but isn't nearly quick enough. He becomes terrified, thinking Yukina might have died, but as the dust clears from the impact, he can see Hiei has pushed Yukina safely out of the way.

Prior to Hiei leaving the Ningenkai for the Makai, Yukina gives him her necklace- a hiruseki stone that her mother cried- and asks him to find her brother, who would also have a hiruseki. In the Japanese text, she also, accidentally calls him "Oniisan"- or brother. Hiei agrees, again refusing to tell her that he really is her brother. He takes her necklace, and eventually gets back his own from the warlord Mukuro.

Editor's Note: For more information about Yukina's age, please see the Editor's Note on Hiei's profile. Also, in Episode 26: Toguro Returns, Hiei states that he and Yukina have different mothers, and are thus half-siblings. However, I'm told that in episodes 99 and 100, Hiei reveals his past and states that Hina gave birth to twins, one which was a boy, thus causing the village elder and another women to figure that Hina violated their rules of complete isolation and conceived Hiei with a man. So, it sounds like Hiei contradicted himself.

INFORMATION FROM ABSOLUTEANIME.COM