That Time I Got Reincarnated as a Slime Novel Volume 13 is written by Fuse with illustrations by Mitz Vah.

The Empire deploys a vast army over 900,000 soldiers strong to invade the Forest of Jura. In response, Ramiris evacuates Tempest’s inhabitants into the Dungeon for safety. While Primal Demons Testarossa and Ultima duke it out with the Empire on the front lines, the rest of the imperial army attempts to invade Ramiris’s labyrinthine shelter. Little do they know, however, that the only thing they’ll find there is a devastating bloodbath courtesy of Tempest’s own mighty forces...