Aincrad (アインクラッド, Ainkuraddo?), otherwise known as Floating Castle of Death (死の浮遊城, Shi no Fuyūjō?), is the first main story arc (第一部, Dai Ichi-bu?) in the Sword Art Online Alternative: Spell Blade Online series.
On November 6, 2022, the first and highly anticipated Virtual Reality Massively Multiplayer Online Role-Playing Game ([[w:c:swordartonline:VRMMORPG|]]) for a special VR console, called the NerveGear, began its official service at 13:00 JST. The game's first 10,000 copies were sold out within moments and about as many players logged in at the moment the official service began. However, the enjoyment did not last long as, several hours later, players noticed that the log out button was not working. Soon afterward, all players were teleported to the [[w:c:swordartonline:Town of Beginnings|]], where an avatar in red robes descended from the sky and introduced himself as the game's creator, Akihiko Kayaba. Akihiko announced to all players that the only way for them to log out was to beat the game by clearing the boss at the end of each floor of the Floating Castle Aincrad. Akihiko then informed the players that all methods of revival were removed from the game and that if they died in the game, someone from the real world attempted to remove the NerveGear by force, or if the NerveGear was disconnected from a power source or the game's servers for too long, the NerveGear would use microwaves to destroy the player's brain. To prove that he was not joking, Akihiko forced every player's avatar to change to their real-life appearance and concluded the tutorial for the game by stating that he had accomplished his desire: to create his own world and control it. This was how the death game known as «[[w:c:swordartonline:Sword Art Online|]]» began.
One of the 1,000 beta testers, named Kirito, began his journey of survival by becoming a solo player and rushing to the nearest village to begin leveling.
Fast-forward two years and the game seems to have almost been cleared on the 75th Floor. A player that was revealed to be Akihiko himself challenged Kirito to a duel. However, Akihiko proved victorious and the hero, Kirito, was martyred. Anguished, Kirin attacked the avatar causing the game to glitch. Soon, it was realized that the game had not been cleared yet. The race to the 76th Floor with the ultimate goal of the 100th Floor begins.