The Emperor has just died and his position remains vacant with no heir appointed before his death, however the world seemingly remains in a state of peace. Utilizing the power of a powerful substance known as aer, the people of the planet Terca Lumireis are in an age of discovery and prosperity. The crystallized form of aer, known as Apatheia, is considered to be a very powerful energy source as it is essential to human life. In order to protect towns from attacks by monsters, large amounts of Apatheia are being produced to create barriers around towns. One day in a deep forest near the town of Shizontania, Yuri Lowell and Flynn Scifo, two knights who have just joined the Nylen Corps, together with two of their senior knights and fellow Corps members, Hisuka and Shastere, are sent on a mission to investigate an abnormal gushing of aer in the area.