There were a forest, called "The Sea of The Dark Trees" or simplifying: Aokigahara. It were a suicide forest, which people who suffered enough always come to suicide. People believe there has ghosts haunting the forest, the souls of the people who died ad people who have killed people. Aoki lost her family as her house were on fire when she arrived, and unfortunately, it was late to save them, and Matsubara, that been abandoned on Aokigahara forest by the family. As those two lives on Aokigahara forest, they believe there's a way to go out of the forest.