Yui (ユイ Yui) is a mysterious girl found by Kirito and Asuna around the forests of the Floria, the 22nd Floor of the Floating Castle Aincrad.
Her official name is «Yui-MHCP001».
Yui is the first version of the «Mental Health - Counselling Program» of «Sword Art Online». She is a «Top-down AI» made to monitor the mental health of the players of SAO. She's a pseudo artificial intelligence built from a program atop an existing computer architecture. Top-down AIs can be considered as a cluster of binary. She later gains access to the real world through a VR probe designed and created by Kirito.
