After taking part in an experiment involving the Soul Translator, a new virtual-reality technology, Kirito awakens in the Underworld with no understanding of how he arrived there. Unable to log out, he discovers a medieval world whose inhabitants seem to possess genuine consciousness. He meets Eugeo, a young woodcutter who tells him about Alice, his childhood friend taken away by the Integrity Knights after breaking a sacred law. Together, Kirito and Eugeo embark on a journey to find her and reach the Central Cathedral. Their quest brings them into conflict with the ruthless rules governing the Underworld, while Kirito searches for the true nature of this world and the reasons behind his presence.