Missing Piece 

High school girl Ai had a strange dream about a childhood past in which she was rescued by a little boy who promised to protect her. The dream seems like a fragment of her memory but she does not have any recollection of the past. Things start to get stranger when there is a guy in her class whom she does not recognize at all. It seems that everyone in the class knows about Akizuki Tohru except for her. Sensing something strange about Tohru, Ai went to conduct an investigation on him and found that the school has no records of him. After confronting him, Tohru eventually admits that he is an ESPer who has infiltrated into the school to investigate on the string of drug-overdose deaths that have been happening in school. This begins the story of Ai's involvement in the life of Tohru and the dangerous events behind the investigation...