After the death of her mother, orphaned high school student Kei Hatō heads for her late father's house in Hemizuka to settle issues with her inheritance. In the train on the way there, Kei has a mysterious dream of a huge tree and a woman who seems to be lost in sadness. In Hemizuka, Kei learns the secret concealed in her own blood through various meeting with an
Oni Slayer, a friend of her late mother, a young girl accompanied by a white fox, and even the mysterious girl from her dreams. Throughout the story Kei is antagonized by the twin oni Nozomi and Mikage. Akai Ito's story varies greatly based upon the player's decisions, which not only affect the flow of the story but also the ending the player receives (several of which suggest romantic feelings among the female characters). ==Character==