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

A hot springs whodunit!

As the Imperial Capital recovers from the rebellion stoked by Inverse Moon, Komari learns that an honors student from the Mulnite Military Academy will be joining her unit as an officer. Esther Claire is kind, considerate, and very excited to be working under the commander she idolizes…but can a straitlaced girl like her really gain the respect of the Seventh Unit's unruly rank and file? Meanwhile, Komari's friends meet in secret to plan her birthday celebration at a hot springs resort in Esther's hometown. But shortly after everyone arrives, a blizzard puts the hotel on lockdown, and a murderer starts killing off the guests one by one! Does Komari have what it takes to find the culprit before she meets a grisly end?