The Citadel, the last stronghold of mankind's resistance against the Apocalypse, has fallen. Humankind is now under the control of the Trumpeters of the Apocalypse, the leaders of the forces of the Apocalypse. The “Martyr” who is the last resort of the Seven Angels, the guardians of humankind, is led by a mysterious signal and sets out on a journey to overthrow the Trumpeters of the Apocalypse. To find the truth behind the signal, buried under the Citadel.