A spirit that was trapping all the spirits of children in the house.

While at school, Taniyama Mai and her friends like to exchange ghost stories. Apparently, there is an abandoned school building on their campus that is the center of many ghost stories. During the story, they are interrupted by a mysterious male figure. The person turns out to be Shibuya Kazuya, a 17 year old who is president of the Shibuya Psychic Research Company. He was called by the principal to investigate the stories surrounding the abandoned school building. 
The next day, on the way to school, Mai passes the school building in question. While examining a strange camera she spotted inside, she gets surprised by Kazuya's assistant. Unknowingly interfering with the investigation, Mai breaks the camera and Kazuya's assistant gets injured. 
Kazuya forcefully hires Mai in order to pay for the camera and replace his injured assistant. From that point on, Mai begins to learn about the paranormal world and the profession of ghost hunting. 
[Written by MAL Rewrite]

An American voice actress who works for anime series of Funimation.

The decrepit building was condemned long ago, but every time the owners try to tear it down, "accidents" start to happen-people get hurt, sometimes even killed. Mai Taniyama and her classmates have heard the rumors that the creepy old high school is haunted-possibly by ghosts from the Second World War. So one rainy day they gather at the told school to tell ghost stories, hoping to attract one of the suspected spirits. 
No ghosts materialize, but Mai and her friends do meet Kazuya Shibuya, the handsome young owner of Shibuya Psychic Research, who's been hired to investigate paranormal activity at the school. Also at the scene are an exorcist, a Buddhist monk, a woman who can speak with the dead, and an outspoken Shinto priestess. Surely one of them will have the talents to solve this mystery! (Source: Del Rey)

Hiro Ooshima