Princess Resurrection

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 of moving up the ladder of succession.