Rui (泪, Rui, in the original Japanese dub; pronounced Ree in the English dub) is an Ice Apparition (氷女, kōrime; lit. ice maiden) who used to be Hina's best friend. She was the one who cast Hiei from the Glacial Village when he was an infant.She was the only one of the Ice Apparitions who actually pitied Hiei. Before she did, she gave him a tear gem that came from Hina, and told him that she wanted him to grow up strong and one day take revenge upon the elders. Then she threw him off of the Glacial Village.

Luckily, Hiei did survive the fall, and was raised by thieves. After Hiei got the Jagan implant, he returned to Koorime to take his revenge as Rui had told him to. The world seemed as if it were dead, the Koorime shutting themselves off from the world for so long. The people lived and behaved as if they themselves were ice, they hardly had feelings, and were all terrified of anyone. Hiei found them too pitiful to kill, thus leaving them to writhe in their own secluded misery.

He found Rui by Hina's gravestone, she then told him about how Hina had committed suicide after the loss of her son (in the manga, she died after giving birth). Rui then also informed him of Yukina and how she left looking for him. After hearing all of this, he left to find her. It is only then that she realizes that Hiei is the same boy that she tossed away all those years ago, and begs him to kill her. He ignores her and walks away, leaving her behind with her guilt and misery.

She is voiced by Yuko Mizutani in the Japanese version. In the English dub, Susan Huber originally provided the voice but her performance was later redubbed by Mariela Ortiz for the Blu-ray version.