Introduction: "Extreme × Despair"! A thrilling ADV (Adventure Game)! One day, 15 students, including "Takumi Sumino", were suddenly summoned to the "Final Defense Academy". Under the orders of "SIREI", who claimed to be the commander, they embarked on a 100-day defense war. Mysterious enemies known as "Intruding Students" suddenly attacked, and there were life-or-death battles. What kind of "truth" lies behind all of this?