Butterfly Knife

The story

A single mother was murdered in a room in an apartment while the news of an indiscriminate murder of women was making headlines every day. At the same time, Kazuki Saito, her son, disappears. The public speculates who could be the culprit and they even have a type, and the police are also looking for him. Meanwhile, a girl named Sayo, wanders into the woods and meets the speculated culprit with a knife. What is the fate of the girl who met the murderer?