Hollow Regalia Novel Volume 4 was written by Gakuto Mikumo with illustrations by Miyuu.

Yahiro and the others journey to Kyoto aboard Galerie Berith's armored train. There, they hope to discover the truth about Japanese people having transformed into moujuu. The train screeches to a halt when soldiers stationed at Nagoya demand a toll-the Regalia: a crimson gem that is…fusing with Ayaho?! There's no way Yahiro or Iroha will hand her over, but how will they keep everyone else safe and escape a barrage of attacks from soldiers and moujuu?