Kirito jumps into a new VRMMORPG called ALfheim Online (ALO) in search of Asuna, who still hasn't regained consciousness.

On his quest to find the World Tree and reach Asuna, he meets a sylph girl named Leafa. A veteran player experienced with the sword, Leafa recognizes that Kirito is motivated by serious circumstances and decides to help him. But...Leafa's identity in the real world is Suguha Kirigaya—Kirito's sister. And it's the glimmer of her beloved brother she sees in Kirito that prompts her to lend him a hand. Now, despite the conflicting interests guiding them on, the pair set off on a journey to the World Tree!!