The Vexations of a Shut-In Vampire Princess, Vol. 10 (light novel) — Kotei Kobayashi

Komari and Spica set out on a journey together with a shared goal: gather the Dark Cores and bring an end to the wars breaking out all across the Netherworld. Komari's other friends who have been warped to the Netherworld try to help, but things go off the rails when a mysterious individual suddenly appears calling himself “the Fool.” This man once ruined Spica's dreams six hundred years ago and now claims he has come to eliminate both her and Komari for the sake of preserving order in the Foreworld. As all the pieces click into place -- the six Dark Cores, Spica's friend from the distant past, and the God Slayer Tower that stands at the center of the realm -- a battle begins that will decide the very fate of the Netherworld!