The dreadful “man-eater” Manticore, recently escaped from a secret facility deep in the mountains, has infiltrated Shinyo Academy and assumed the form of one of the students. With the help of another student, she feeds on students passed off as runaways while setting up a diabolical plot with greater aspirations. The inhuman being called Echoes seeks her out to stop her, though, while high school student Kirima Nagi and a mysterious figure known as Boogiepop, an alleged “angel of death” spawned from another Shinyo Academy student, also opposes her efforts. Into this environment of danger and intrigue several other students are drawn, some as witnesses or associates of those involved, other as active participants or even victims.
from ANN

Notes

Alternative Names/Des Noms Alternatifs: Boogiepop wa Warawanai
Author: KADONO Kouhei
Artist: OGATA Kouji
Genre: Drama, Horror, Mystery, School Life, Supernatural
Demographic: Seinen
This is the light novel which was the basis for Live Action film and the anime series, Boogiepop Phantom.
Adapted into the anime/Adapté dans l'anime Boogiepop wa Warawanai