Sword Art Online Alicization Uniting Novel Volume 14 is written by Reki Kawahara.

Kirito has faced innumerable hardships in the two long years since he first awoke in the Underworld, but his greatest battle yet lies ahead. As they near Administrator's chamber at the top of Central Cathedral, Kirito and Alice confront a heartrendingly familiar foe on the ninety-ninth floor. The final obstacle standing before them is none other than Eugeo...wearing the armor of an Integrity Knight! Can Kirito's cries reach Eugeo in the tortured recesses of his mind? Or will Administrator have the last laugh?!