The Vexations of a Shut-In Vampire Princess, Vol. 6 (light novel)  (English, Paperback, Kobayashi Kotei)

There's a new face in the Komari unit! Though Komari is initially worried that Esther, an honors student from the Mulnite military academy, will be abused by her unruly subordinates, it turns out that the recruit is plenty unhinged herself. Before long, Komari's long-awaited break from work arrives, and she just so happens to spend it at a hot springs resort in Esther's hometown. But unbeknownst to her, a sinister plot is steadily unfolding in this seemingly idyllic village...