Eve of War

Eve of War (戦争前夜編) is the twelfth volume of the That Time I Got Reincarnated as a Slime Light Novel.

Synopsis
Threatened by Tempest’s rapid expansion, the Eastern Empire finally begins to strike back. According to Chloe, the time-traveling Hero, there exists a timeline in which the Empire defeats Rimuru and Tempest subsequently collapses. While Rimuru’s doom isn’t set in stone, his victory isn’t a foregone conclusion either. And to make matters worse, an Empire spy seems to have infiltrated Tempest...

Chapters

 * Chapter 1: The Stepping Sound of Military Boots
 * Chapter 2: Results and Preparation
 * Chapter 3: Visitors from the Empire
 * Chapter 4: The Empire is Out
 * Chapter 5: Before the War