Before Chise assumed the mantle of the 'ultimate weapon,' there was Lieutenant Mizuki, a seasoned military figure who underwent an experimental transformation due to battlefield injuries. Although excelling in combat as the pioneering ultimate weapon, Mizuki's potential was restricted as the initial subject. When Chise, a more fitting candidate, is reluctantly thrust into the military program, Mizuki views her as naive and unfit for the role. Despite these reservations, Mizuki, the sole individual familiar with the procedure, can delve into Chise's innermost thoughts, fostering a unique understanding. Amidst the turmoil of war and Chise's evolution, Mizuki embarks on a journey of self-discovery, unraveling the mysteries surrounding Chise, the ultimate weapons, and her own identity.