Spirosaurs are fantastic creatures born in the world of "Isolation." Those who fight them are called "Periods." Haru is a student of a period, assigned to the Eighth Division of an organization called "End of the Arc." One day, a mysterious theft triggers an "economic collapse," and the headquarters abandons the Eighth Division to fate, leaving only three periods there, including Haru. Now these three must work together to restore their home division.
