The Vexations of a Shut-In Vampire Princess, Vol. 4 (light novel) — Kotei Kobayashi

Fresh off her success in the Six Nations War, Komari is invited to the Heavenly Paradise, a Far Eastern nation where cherry blossoms dance in perpetuity. There, she learns that one of her new allies, Karla Amatsu, is participating against her will in a weeklong ritual to determine the next ruler of the country.
Always looking to shirk her duties, Komari writes the whole thing off as someone else's problem…until Karla announces that the vampire girl will be assisting her in a battle to the death against the opposing candidate on the final day of the competition! But with multiple foreign parties attempting to influence the outcome of the proceedings and a terrorist plot developing in the background, can these two reluctant commanders really come out on top?!