Two years ago, Akagi Kei's older brother Keiichi, who was a policeman with a bright future ahead of him, mysteriously vanished. The police eventually closed the case, but they never found any sign of what happened to her brother. After that, Kei was very busy as the oldest child in the house, especially since her mother worked nights, so it took her a while to recognize a strange new voice that was calling to her...

It was her brother, or at least her brother's skeletal ghost. Now she knows that her brother is dead, but she doesn't know how or why. He seems lost and confused, and says that he has come from a dark forest full of the dead that have a grudge against the living. For his part, as in life, he wants to help people and to protect his little sister Kei. Kei is just starting in a prestigious high school, where it seems that there is more than a fair share of supernatural darkness creeping into the student body. Kei and her brother use the skills of the living and the dead together to solve the mysteries behind her schoolmates' problems. Perhaps one day, Kei will also be able to solve the puzzle of her brother's death.