There is a world where fantastic beasts called “Spirals” are born from isolation. Those who can defeat the beasts are called “Periods“. Haru is an apprentice Period who belongs to the Arc End 8th Branch. However, after a mysterious theft incident, there is an economic collapse, and the Arc End headquarters abandons the 8th Division, leaving only three Periods left, including Haru. Haru and the other two Periods start their work to rebuild the 8th Division.