Sword Art Online Novel Volume 26 is written by Reki Kawahara.

On the 80th floor of the Central Cathedral, Kirito, Asuna, and Alice have a reunion with dear friends, but Kirito is pulled away to Planet Admina to investigate the approaching threat to the Underworld. Meanwhile, in Unital Ring, Sinon, Silica, and company are putting up a good fight against the field bosses, but the conflict intensifies in a way few could have predicted…