In a cutting-edge virtual world, the Soul Translator connects with users' Fluctlights, akin to human souls, diverging from traditional brain signal transmissions. Rath, a secretive institute, recruits Kazuto Kirigaya, a survivor of Sword Art Online, to refine their technology. Kazuto delves into the Underworld, a mystical domain of the Soul Translator, as a part-time tester, bound by a strict non-disclosure agreement erasing virtual memories upon exit. Haunted by the elusive name 'Alice,' Kazuto's tranquility is shattered when a chance encounter leads to a fateful confrontation where he sustains grave injuries. Awakening within the Underworld, trapped and disoriented, Kazuto embarks on a perilous journey to navigate this alternate reality and uncover a path back to his physical existence.