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Artificial Intelligence (or A.I.), in the field of gaming and computer science, refers to the intelligence of the machines and the effort to re-create human-like intelligence in Non-Player Characters (NPCs).
In Sword Art Online, the system is generally known for having a mixture of NPCs with very advanced A.I. and NPCs with very poor A.I.
In the Sword Art Online Universe, a Top-Down AI refers to artificial intelligence built from a program atop an existing computer architecture. NPCs in SAO have top-down AI, meaning they are scripted to act in an exact certain way in response to a very specific stimulus.
When speaking to Top-Down NPCs in a quest, a player must listen to the NPC through the entire duration of the speech. If not, the quest does not proceed, as the Top-Down AI is scripted in a very basic, simplistic fashion.
Top-Down AIs work from an answer, and wait to respond to a question. Some AI can even be scripted and modeled to mimic human behavior, to almost be indistinguishable from a human. These AI simply have more data to process, and have learned to mimic behavior, to fit a personality. Yui is a prime example of a very advanced Top-Down AI.
If a player tries to touch an NPC in any way, they will momentarily receive a warning message for harassing the NPC and will get shocked. This is to prevent players from moving them to a player's desired location or sexually harassing the NPC. This, however, does not happen to Yui, as her position in-game is not fixed to any specific location.
In Sword Art Online, NPCs can be killed much like players, but unlike players, NPCs will respawn after twenty-four hours. However, there are two exceptions. First, «Tamed Monsters», such as Pina, turn into a «Heart» upon their death and can only be resurrected with the «Pneuma Flower», but this can only be done within three days after its death, otherwise the heart becomes «Remains», in which case, it cannot be revived at all, effectively making the Tamed Monster permanently dead. Second, Yui is classified as an «Immortal Object» and therefore cannot be harmed at all.
Bottom-Up AI are AI that work in the opposite manner of a Top-Down AI, as they compute an answer when a question is given, rather than having a preset answer to a desired question. Unlike Top-Down AI, who learn by the "Ask A, so answer with B" method, Bottom-Up AI learn through "Learn B, and answer when asked A". According to Kirito, this is what a true artificial intelligence should be like.
In the Sword Art Online Universe, the only known way to create a Bottom-Up AI is through the cloning of a human Fluctlight - creating an Artificial Fluctlight. An Artificial Fluctlight is the cloned quantum field (soul) of a newborn baby, which is later nurtured in a VR world.
List of known AIs/NPCs
- Angel - Quest NPC for the Angel's Ring quest.
- Kizmel - A Dark Elf knight on the 3rd Floor and original questgiver for the Dark Elf path of the Elf War campaign.
- Leviathan the Sea Lord - Quest NPC that interferes with the fight between the players and Kraken the Abyss Lord at the end of the Deep Sea Plunderers Quest.
- Leyshren Zed Yofilis - Head of Yofel Castle on the 4th Floor.
- Nerakk - Quest NPC that gives players the Deep Sea Plunderers quest, requesting players to retrieve a pearl stolen from him by thieves that hid in the Undersea Temple. If players discover that the "pearl" is actually an egg and refuse to give it to Nerakk, he transforms into Kraken the Abyss Lord and fights the players.
- NPC Orchestra - NPCs providing background music in Aincrad.
- Pina - Silica's Feathered Little Dragon companion.
- Romolo - A former shipwright on the 4th Floor and questgiver for the Shipwright of Yore quest.
- Ruru - An NPC on the 56th Floor who provides the secret of defeating the Field Boss.
- Skuld - Quest NPC for The Holy Sword of the Ice Palace quest.
- Thor - Quest NPC for The Holy Sword of the Ice Palace quest.
- Thrym - Quest NPC for The Holy Sword of the Ice Palace quest.
- Tonky - A Beast-type evil-god monster in Jötunheimr, which later turns into an NPC capable of transporting players on its back.
- Urðr - Quest NPC for The Holy Sword of the Ice Palace quest.
- Some Vendors on streets.
- Underworld Residents (excluding Kirito).
- Verðandi - Quest NPC.
- Yui - In-game foster daughter of Kirito and Asuna and a former Mental Health Counseling Program.
- YUNA - An augmented reality AI idol.
- Afasys - Game adaptation-exclusive AI companion of the Protagonist.
- Daisy - Game adaptation-exclusive AI companion of Zeliska.
- Lievre - A game adaptation-exclusive AI companion of Subtilizer.
- Persona Vabel - Game adaptation-exclusive alternate future version of Yui.
- Premiere - One of the game adaptation-exclusive NPC twins originally designed as part of the Ground Quest of Sword Art: Origin.
- Tia - One of the game adaptation-exclusive NPC twins originally designed as part of the Ground Quest of Sword Art: Origin.
- Strea - A game adaptation-exclusive former Mental Health Counseling Program.