This man appears in Rain's flashbacks, and his role and purpose are gradually revealed throughout the series. His primary objective is to end human life, as he is reincarnated each time he dies, always returning as another human being. Yuca is the reincarnation of Methuselah's spirit, a name later applied to Rain. He desires eternal death, but the only way to ensure it seems to be by eliminating all human life that could reincarnate him.
He reincarnates as Ishmael's son; his mother, who is Sharem's sister, dies immediately after giving birth to a child already in the form of a young boy. Sharem names him "Ys," believing he is the reincarnation of her deceased son. Having experience creating "angels" in his previous life, Ys recreates these destructive devices during his current life. He was responsible for Freya's death and the production of biological weapons, as well as Rain's immortality. He wants Rain to experience his pain and understand the despair of being who he is.
In a later volume, it is suggested that a part of Yuca secretly hopes Rain will stop him.
