Kumiko Hayakawa and Keiko, whose parents had died three years earlier, lived together, cuddled up to each other. One day, when they arrived at a corner of a multi-tenant building, Keiko disappeared to buy sanitary products, and Kumiko got on the elevator alone. At that moment, three men entered the elevator as it was closing. A strange atmosphere prevailed. An unbelievable scene unfolded...

One day, a mysterious letter 'F' starts to be written on doorplates in a condominium building. Since then, mysterious incidents consistently occur around Yukari Yamamoto, who is an ordinary female high school student living in the building.