The series follows Kou Ootori, an ordinary high school student who experiences a recurring nightmare of being eaten alive by a beast from within. However, when he meets Reiichi Kuki, an upperclassman who controls the school, the curtain of fate unravels.

Chimera incident, a serial murder and explosion crime that shook the year of 1984, takes place exactly the same thirty five years later in 2019. Just like the terrible explosion in the past, the murder of the crime is called Chimera, a monster in the Greek myth with the head of a lion, body as a goat, and tail as a snake that shoots fire through its throat.