The Forlorn Hope (暗黒鏡, Ankokukyō, literally translated as Darkness Mirror, VIZ translation, Mirror of Darkness) is one of the three Artifacts of Darkness. It's held in a vault within the depths of Spirit World and is considered a dark artifact because it grants any wish that its user may have, but at the price of the user's life.
Kurama stole this artifact from Gouki and Hiei for the express purpose of curing his mother, Shiori Minamino, of her longlasting illness. Knowing full well the price that the Forlorn Hope demanded, he was ready to sacrifice his new life. At the last minute, however, Yusuke intervened and ordered the mirror to take his life instead of Kurama's.
Impressed by such a willingness to sacrifice his life for Kurama's, the Forlorn Hope cured Shiori's illness without killing Kurama, or Yusuke for this deed (For the English manga and Japanese versions, the mirror only took half of the life-force from both Yusuke and Kurama to fulfill the wish by splitting the difference). It was returned to the Vault at the end of Yusuke's first mission as Spirit Detective, though not before Yusuke used the mirror as a reflective surface to bounce his Spirit Gun at Hiei's back which shattered it.
- The Funimation name, Forlorn Hope, is derived from the term for the first wave of soldiers attacking a breach in defenses during a siege. In general, members of a forlorn hope are cannon fodder expected to be killed or badly wounded.
- The Forlorn Hope is based on the Yata no Kagami (八咫鏡 Yata no kagami, literally translated as Eight Hand Mirror), one of the three sacred treasures of Japan. The Yata no Kagami is said to represent wisdom and honesty.
- Given the loophole that saved Yusuke and Kurama, it's possible the spirit in the mirror would be willing to accept the offer of another's full life instead of the wisher.