A young man named Tsukasa, who goes by an online pseudonym, wakes up with vague memories within the MMORPG The World. He is suspected of hacking since he was seen with a modified cat-like character. With no way to log out, he wanders the game world while avoiding other players and the Crimson Knights, who think he's an enemy. During his journey, he stumbles upon a powerful item called a guardian that promises to keep him safe. Subaru, the Crimson Knights' leader, and other players who have befriended Tsukasa decide to investigate his predicament before it becomes too late.