Horror and mystery go together, certainly. But adding emotional aspects to them takes courage along with skills. And that can be found in “Claymore”. The manga is written and illustrated by Norihiro Yagi. You might not know him yet but you should.
The theme of the manga is based on human shape-shifters, called “yoma”. They are more like poltergeists or monsters. The difference is that yoma can take the form of people or corpses.
The story starts with a yoma who remains hidden in an area. The mystery goes a notch up with “claymore” arriving on the scene. A lovely lady in armour with a 5-6 feet tall claymore (broadsword) – what is her purpose? What is her race? Why did she come here and why do people hate her so much? These questions will all plague you at first.
The ladies are called “claymores”, after their swords. And inside them, reside yoma. It is the source of a claymore's power. But if it goes out of hand, it transforms the claymore. They may become the most powerful yoma, called “awakened beings”. When this happens, they can rule lower-tier yomas. All of them belong to a third party called “The Organisation”, who takes care of their needs. But the existence of The Organisation and the authority level is a matter of mystery too.
So, their own existence is a threat towards themselves and towards the human kind. That's why they are called claymores; the double-edged blades can cut both sides.
A claymore can still love, that's what we can see from the first episode of the anime. The action is magnificent as they show the true beauty of sword-fighting.
The anime, as of yet, is 26 episodes long, produced by Madhouse, who were the producers of Death Note. That should be motivation enough for a lot of people to pick it up. The director Hiroyuki Tanaka managed to mix horror, mystery action and romance all into one anime efficiently.