Ruka is a barrier creator and nurse in the Dark Tournament. She was to keep Hiei and the Masked Fighter occupied during the fight between Team Urameshi and the Shadow Channelers.

Urameshi Yusuke, 14 years of age, is about as troublesome and violent as teenagers come. He is constantly ditching school, causing trouble, and getting into numerous fights everyday. One day however, he does the unexpected, sacrificing himself to save a young child. Such an action, was never ever expected, especially coming from someone as troublesome as Urameshi Yusuke. The afterlife is not prepared for Yusuke, as they never thought he would make such a sacrifice. Nowhere to go, and dead, Yusuke becomes a ghost and must earn his way back into existence. 
Yusuke is "employed" by Koenma, who is in charge while his father and ruler of the afterlife, King Enma, is away. Under Koenma's command, Yusuke helps to stop menacing demons that threaten the lives of people everywhere; whether by stealing priceless and invaluable items and destructive weapons, or by wreaking havoc on humans everywhere. 
Throughout Yusuke's journey, he is usually joined by; his arch-rival, and local bully, Kuwabara Kazuma. He is also joined by two demons named Hiei and Kurama, whom are ex-convicts of the afterlife that managed to escape from Koenma. 
This group of unlikely allies goes on to participate and struggle in battles that have outcomes that determine the fate of humanity! 
(Source: AniDB)

Suzuka Chiharu is a freelance voice actress who previously worked under Ken Production.

Yusuke Urameshi was a tough teen delinquent until one selfless act changed his life...by ending it. When he died saving a little kid from a speeding car, the afterlife didn't know what to do with him, so it gave him a second chance at life. Now, Yusuke is a ghost with a mission, performing good deeds at the behest of Botan, the ferrywoman of the River Styx, and Koenma, the pacifier-sucking judge of the dead.
 
(Source: Viz Media)
 
Note: Volume 7 contains the special story "Yuu Yuu Hakusho Tales: Two Shot" (外伝. TWO SHOTS)