From Dazzling Scans:

The country of Japan is being terrorized by the undead, known as Revenants. Tachibana Kaguya makes it her life goal to protect her fellow citizens from these zombie-like creatures, just as her father did before her. When she enrols in Reimeikan Academy, a school that specializes in training soldiers that will eventually become part of a movement to expel the Revenants once and for all, she is reunited with Tokugawa Kazui... a boy her father had died to protect—a boy who had promised to build her a world free of monsters.