Following on from the previous film, Sword Art Online: Progressive – Aria of a Starless Night, the main characters, including Kirito (voice of Yoshitsugo Matsuoka) and Asuna (voice of Haruka Tomatsu), have made it to the fifth floor of an on-line game where the players are trapped inside and are not only fighting for their lives in the game but also for their real lives beyond it. There are two main guilds battling each other for leadership status; rogue individuals trying to kill off players; and virtual monsters and ghosts to fight in the dungeons and catacombs. Consequently, Kirito and Asuna work together to organise a small group to outmanoeuvre the warring guilds, destroy the floor boss and level the playing field, giving each trapped individual an equal chance at survival. The only problem is that the game is adapting and intent on destroying them all. Will Kirito and Asuna succeed or will they perish in the process?

One month after Kayaba Akihiko's game of death began, the death toll continues to rise, two thousand players having already lost their lives to the ultra-difficult VRMMO world of Sword Art Online. On the day of the strategy meeting to plan out the first-floor boss battle, Kirito, a solo player who vows to fight alone to get stronger, runs into a rare, high-level female player. She gracefully dispatches powerful monsters with a single rapier that flashes like a shooting star in the night...

Source: Yen Press

Rinko informs Kazuto that Alice is missing. He's about to rush to the Rath Roppongi branch when the doorbell rings. In a panic, Kazuto throws open the door, only to find a deliveryman there with a huge cardboard box.

The "Rath Attack Incident," masterminded by the American National Security Agency, is over. Now head of the newly formed Oceanic Resource Exploration & Research Institution, Rinko unveils Alice to the world as an authentic artificial general intelligence.

The maximum-acceleration phase has begun. Alice successfully logs out of the Underworld, but Kirito doesn't make it in time. In the real world, Higa and Kikuoka rush to shut down the STL, in order to disable the maximum-acceleration phase, but…

Alice and Asuna head to the World's End Altar as Kirito confronts Gabriel. Unless he can defeat Gabriel and return to the real world before the maximum-acceleration phase begins, Kirito will have to spend the next 200 years in the Underworld.

Escaping his nightmares, Kirito regains consciousness at last. With the Night-Sky Blade in his right hand and the broken Blue Rose Sword in his left, he faces off against Vassago, armed with the Mate-Chopper, now enormous in size.

Sinon manages to severely damage Gabriel, but her strength has been sapped. Leafa collapses after wiping out the American players. And Asuna, her situation now hopeless, gazes at Kirito. But the Black Swordsman continues to wander through his dreams.

Asuna and the others succumb to Vassago and the Chinese/Korean players. Discovering the catatonic Kirito, Vassago kicks his wheelchair over. Enraged, Klein lunges at Vassago, only to be pinned down by enemy players. Just then, someone unexpected appears.

The traitor inside Rath turns out to be a researcher named Yanai. When Higa attempts to restore Kirito, Yanai tries to thwart the operation by holding him at gunpoint. Meanwhile, in the Underworld, Sinon confronts Gabriel, who has logged back in.

Bercouli pursues Vecta, who's abducted Alice. After a long, vicious battle, Bercouli unleashes his secret sword skill, Uragiri, and finally defeats Vecta, despite having sustained severe injuries himself.

Despite its modest size, the Human Empire Army and Asuna valiantly battle the wave of American players surging towards them. But they're hopelessly outnumbered, and the Human Empire soldiers start to fall one after another.

The ice sniper from Gun Gale Online, Sinon, successfully logon into Underworld using a super account Solus, the goddess of the sun, to help Asuna and Kirito inside the Underworld against tons of Crimson Army and The Dark Knight.

Due to Gabriel's scheme, U.S. players were given black knight accounts, and are now continuously logging in to the Underworld. They begin mercilessly slaughtering soldiers from both the Human Empire Army and the Dark Territory Army.

Asuna has created a bottomless chasm. The dark knights and the pugilists attempt to cross over to the other side, where the Human Empire Army waits.

Asuna has logged into the Underworld using the superuser account of Stacia, the Goddess of Creation. After she descends, she is reunited with Kirito, thanks to Ronie and Tiese. But soon Alice arrives, leading to a precarious situation.

Upon seeing Alice, Gabriel orders his entire army to capture her. The pugilists guild races ahead of the main force. As Alice and Bercouli try to come up with a strategy to counter them.

The powerful formal art unleashed by the Integrity Knight Alice inflicts severe casualties on the forces of darkness. Alice encounters an enemy survivor and learns that Emperor Vecta's objective is to find the "Priestess of Light."

Integrity Knight Renly Synthesis Twenty-Seven, in battle for the first time, flees his position, allowing goblins from the forces of darkness to infiltrate to the tent where Kirito is.

The Final Load Test has begun, and the Eastern Gate has collapsed. Incited by Gabriel, now Emperor Vecta, the massive army of the land of darkness pushes on towards the Human Empire.

Resolved to fight for humankind, Alice joins the forces of the Human Empire, bringing Kirito with her. But while the forces of darkness boast overwhelming numbers, only thirteen Integrity Knights are available to fight for the Human Empire.

Shasta, commander of the Dark Territory's dark knights, had intended to use Administrator's death as a chance for peace with the Human Empire. But his plans are thwarted by Emperor Vecta's return to the land of darkness.

The mysterious group that attacked the Ocean Turtle turns out to be a secret unit under orders from the U.S. National Security Agency. And its leader, Gabriel, has battled Kirito and Sinon before.

A force from the Dark Territory is attacking Rulid Village. Though she'd lost her purpose in battle, in order to fight for her family, and for the people that Kirito and Eugeo tried to protect, Alice takes up the Osmanthus Blade once again.

Six months have passed since the fierce battle against Administrator. Alice has brought Kirito to her childhood home, Rulid Village, where they live peacefully. Gazing out at the world that she saved with Kirito, Alice reflects on all that's happened.

The anime will also have a compilation episode for Sword Art Online: Alicization titled "Reflection" that will run on Tokyo MX, BS11, Gunma TV, and Tochigi TV on October 5. It will then run on AT-X on October 6, on MBS on October 7, and on TV Aichi on October 12, and it will stream on AbemaTV on October 12.