The main character in Volume 7. She was an Imp in ALO, she started dueling anyone promising an 11-hit OSS if she's defeated; due to her undefeated status she's given the title 'Absolute Sword'. Eventually Asuna fights her but loses. After the fight Yūki asks her to help defeating the 27th floor boss with her guild the Sleeping Knights. After certain events, which include the defeat of the 27th floor boss it is revealed that Yūki has AIDS and the Sleeping Knights members were patients in terminal state; with the time passing Yūki's condition gets worse and after she entrusts her OSS Mother's Rosario to Asuna she dies peacefully in ALO, surrounded by over 1000 players from every tribe in the game, including her guild members, Asuna and her friends.