Sword Art Online: Alicization

Rath’s experimental full-dive system, the Soul Translator, doesn’t just feed signals to the brain—it interfaces directly with a person’s Fluctlight, a technological stand-in for the human soul. To refine the project, the institute recruits Sword Art Online survivor Kazuto Kirigaya as a part-time tester, sending him into the Underworld, a vast fantasy realm created through the device. Bound by strict confidentiality, any experiences he gains there are meant to be erased upon returning, leaving only a faint, unsettling trace of one name: Alice.

After walking Asuna Yuuki home one night, Kazuto and Asuna run into a familiar enemy, and the confrontation leaves Kazuto gravely injured. He awakens to find himself fully immersed in the Underworld—and unable to log out—forcing him to press forward through its world in search of a way back to reality.