Kaibutsu Oujo (OVA)

When Hiro Hiyorimi tries to save a beautiful young woman from certain death, he ends up a dead hero himself! However, since the drop-dead girl is Hime, daughter of the King of the Monsters, his "reward" is to come back as a not-quite-living soldier in her honor guard of horror! That means helping fight off the army of supernatural monstrosities Hime's siblings are unleashing against her in hopes…