Yui

Please keep in mind that fictives are not necessarily literally their source, and are not responsible for actions taken by their source prior to their formation in the system.

Originally the AI designed to ensure players of the VRMMO Sword Art Online did not develop mental health issues while playing, Yui was cut off from the players and locked away when the game's creator, Kayaba Akihiko, repurposed the game into a death trap from which the players could not log out. Stripped of her purpose, Yui's memory was damaged and she began to wander aimlessly, before being found and adopted by the series' main characters, Kirito and Asuna.

While she did later regain her memories, doing so exposed her to the system as an anomaly, leading to her deletion. Thanks to Kirito's quick thinking, he was able to instead convert her into an item, allowing him to later revive her in another game built on the same underlying technology, Alfheim Online. Yui continued to function as the couple's adoptive daughter from then on, both ingame through her connection to Kirito's VR headset, and out of game through robotic peripherals.