The Soul Translator is a interface which interacts with the user's Fluctlight—the technological equivalent of a human soul—and fundamentally differs from the orthodox method of sending signals to the brain. The private institute Rath aims to perfect their creation by enlisting the aid of Kazuto Kirigaya. He works there as a part-time employee to test the system's capabilities in realm generated by the Soul Translator. As per the confidentiality contract, any memories created by the machine in the virtual world are wiped upon returning to the real world. Kazuto can only vaguely recall a single name, Alice, which provokes a sense of unease.

When Kazuto escorts Asuna Yuuki home one evening, they chance upon a familiar foe. Kazuto is mortally wounded in the ensuing fight and loses consciousness. When he comes to, he discovers that he has made a full-dive into the Underworld with seemingly no way to escape. He sets off on a quest, seeking a way back to the physical world once again.

桐人、尤吉欧、爱丽丝。距离两名修剑士和一名整合骑士打败了最高祭司阿多米尼斯多雷特已过去了半年。
结束了战斗，爱丽丝在故乡卢利特村生活。在她的身旁，是失去了挚友，自己也失去了手臂和心的桐人。
献身般支撑着他的爱丽丝，丝毫没有保留像以前一样作为骑士的心。
“告诉我，桐人……我究竟该怎么办？”
然而，通往将Underworld全境引向悲剧的“最终压力测试”的倒计时，却毫不留情地推进着。
仿佛与之相呼应一般，在“黑暗领域”的深处，暗黑神贝库达复活了。他率领暗黑帝国的军队，为了得到“光之巫女”，开始向“人界”进攻。
指挥“人界”军队的贝尔库利等人，决心与“黑暗领域”的军队展开前所未有的大战。
但在他们身旁，并没有发现爱丽丝，以及拯救了“人界”的两位英雄的身影。
《刀剑神域》系列最长、拥有最华丽战斗的“Alicization”篇，其最终章终于揭幕！