Sword Art Online Novel Volume 23 is written by Reki Kawahara.

The moment Kirito, Asuno, and Alice were dragged into the mysterious VRMMO “Unital Ring,” Shinon was also thrust into the online world. After numerous setbacks, she finds herself without friends or equipment, and only a few “Thirst Points” left to her name. Backed against a wall, she’ll need to defeat a terrifying boss monster to survive. Meanwhile, Kirito’s group splits in order to both search for Shinon and defend their home, unaware that a mysterious assailant lies in wait...