Long before becoming the infamous "Reaper" of the Commission of Counter Ghoul, a young Kishou Arima was once assigned to attend high school in order to investigate a series of murders caused by a ghoul with a fervent appetite. What was supposed to be a solo mission changed very quickly for the young genius as he became involved with his delinquent classmate Taishi Fura.

When Fura witnesses the brutal death of his best friend at the hands of a masked ghoul named "Lantern," it seems certain he will meet a similar fate. At the last minute he is saved by Arima, giving Fura a glimpse into the world of a ghoul investigator. Although the ghoul escapes, Fura decides to join forces with his savior and classmate, vowing to bring Lantern to justice.