Yui's Heart

Kirito, Asuna, and Yui are resting at the church, where Sasha takes care of the younger children, until Yulier, second-in-command from the Army, suddenly arrives. Yulier explains that the Army under their leader, Thinker, had good intentions of helping players but as the Army grew, its members began abusing their powers. Thinker was going to expel Kibaou over the Gleam Eyes incident, but the latter trapped him in a secret dungeon on the first floor. Yulier asks Kirito and Asuna for help in the rescue. They arrive at Thinker's location in the dungeon, and are attacked by a boss called the "Fatal Scythe". As the boss is about to strike down Kirito, Yui jumps in between them. The boss attacks, but is unable to damage her because she is an "Immortal Object", which means the system will not allow her to take any critical damage. Yui recovers her memories, and reveals herself as artificial intelligence, a simulation of human-like intelligence and behaviors. Despite the revelation, Asuna and Kirito still accept Yui as their "daughter", but Yui bids them farewell when she realizes that she is going to be deleted for her interference in the game. Refusing to accept her deletion, Kirito uses the Gamemaster console Yui left behind to save Yui's data to a game item, "Yui's Heart".