Akahyou no Sanctuary

Takatou is rescued after a mountain accident by Ritsu, a woman with a red mark beneath her right eye, who warns him of the danger of revealing their secret. He later learns about the legend of the Red Leopard, which speaks of a substance that can be turned into an elixir. Takatou becomes fixated on finding Ritsu again, leading to a romantic relationship between the two, who are bound by the mystery of the legend.