Kirito and the boss raiding group manage to slay the Skull Reaper, but with fourteen high-level players dead, morale begins to drop sharply as the players start to wonder if they can make it through the remaining twenty-five floors with the bosses on those floors being more powerful than the Skull Reaper.
Kirito then notices something odd: all of the surviving raiding party members are exhausted and low on HP, save for Heathcliff, whose HP is still in the green zone and who appears completely composed. Remembering their duel where Heathcliff managed to avoid an attack with a speed that should not be possible in the game, Kirito suddenly attacks Heathcliff, but his attack is deflected by an invisible shield: as a tag indicates, Heathcliff is an "Immortal Object", something that the other players take notice of, leaving them perplexed.
Kirito explains that Heathcliff's "Immortal Object" status means that his HP meter cannot drop into the yellow zone, and points out something he had always wondered: what was Akihiko Kayaba, the game's creator, doing since the beginning? Kirito had believed he was just watching everyone else play, but he has come to the realization that Akihiko Kayaba would not be content to watch: he would have joined the game and had fun along with the other players. So he inserted himself into the game as Heathcliff.
Heathcliff confirms that Kirito's suspicions are correct: he is Akihiko Kayaba. Everything that had happened up to this point is part of a narrative he had hoped to convey. When the players made it to the 90th floor, he would have betrayed the Knights of Blood and everyone else, then set up himself in the final dungeon on the 100th floor so as to serve as the game's final boss. Kirito was meant to become the "hero" of the story, as represented by his Dual Blades skill, awarded to the player with the fastest reaction time.
Shocked by the reveal, one player attempts to attack Heathcliff, but he uses his GM privileges to protect himself and put everyone under paralysis, save for Kirito, who asks if Heathcliff plans to kill everyone that knows the truth. Heathcliff, however, states that doing that would be unfair, since there would be no one to end the game then, so he plans to go ahead in his plans. Before leaving, though, Heathcliff offers Kirito one last chance to end the game: a duel to death. If Kirito wins, the game ends, and everyone still alive will be liberated. And, in order to make it fair, he disables his protections.
Asuna tries to protest, but Kirito accepts the challenge. After saying his farewells to Klein and Agil, he asks Heathcliff to prevent Asuna from killing herself, should he lose (much to her distress), and then the two begin. The two duellists fight, with Kirito's rapid strikes being countered by Heathcliff's shield while the latter cannot attack much, and Kirito relying purely on his strength and instincts, because using a sword skill would allow Heathcliff to counter the attack. However, in his attempts to land a hit on Heathcliff, Kirito accidentally activates a sword skill, which Heathcliff blocks by breaking one of Kirito's swords.
Before Heathcliff can finish Kirito, though, Asuna manages to overcome her paralysis by sheer force of will and jumps between them, taking the final blow. Kirito is struck hard by this, and he loses the will to fight, allowing himself to be run through. As his HP drop to zero, he remembers Asuna's words of encouragement and, by sheer force of will, manages to remain in the game long enough to take Asuna's rapier and stab Heathcliff, driving his HP to zero. Thus, on November 7th 2024, Sword Art Online is officially cleared.
Kirito awakens in the sky over Aincrad, and finds Asuna there as well, miraculously alive. As they grab onto each other, relieved to at least be together once more, they are joined by Kayaba, now looking like his real self. Kayaba explains that the game's servers are self-deleting themselves, and that the approximately 6,000 surviving players have started to log out of the game, but those who died in game are gone forever. When asked why he did everything, Kayaba says he doesn't remember, but he recalls a dream he had about a castle floating in the sky, and wished to make something similar, a castle where he was free from the laws and restrictions of the real world. After congratulating Kirito for winning SAO, he departs forever.
As they watch the end of Aincrad, Kirito and Asuna share a promise to meet again, and also their real identities: Kazuto Kirigaya, age 16, and Asuna Yuuki, age 17. The two embrace in a kiss as they are engulfed in a white light, and their avatars disappear...
Kazuto awakens in his hospital room, alone. After being two years of being hooked to the NerveGear and kept in a coma, his body has become weak and emaciated, and his hair has grown down to his back. After a moment of disorientation, he remembers Asuna, and manages to stand up with the strength he can muster, clutching his IV drip for support, and ready to find her, wherever she is...
- Chekhov's Gun: The incident during their first duel where Heathcliff was able to move a lot faster than the system should have allowed is what began to clue Kirito in that Heathcliff is not who he claims to be.
- The "shared storage through marriage" feature from "Illusionary Avenger" returns, allowing Kirito to use Asuna's rapier to kill Kayaba.
- The fact that players actually don't die until ten seconds after losing the last of their HP, revealed in "Red Nosed Reindeer, is what allows Kirito to survive, as Kirito manages to clear the game by killing Kayaba before his ten seconds are up.
- Determinator: After finally logging out after two years in Aincrad, Kirito only has one objective: to find Asuna, whatever it takes. Even if he's weak and emaciated.
- Fair-Play Villain: Kayaba offers Kirito the chance to fight him in a duel after being discovered, taking off all his admin privileges to make the duel fair.
- Heroic BSoD: After Asuna jumps to take a lethal blow for Kirito, he loses the will to fight.
- Heroic Second Wind: In his last seconds of life, Kirito decides that he will not go out without finishing the game, and stabs Kayaba with Asuna's rapier.
- Taking You with Me: Just before he dies, Kirito manages to kill Kayaba - clearing the game and, incidentally, saving both his and Asuna's lives.
