Tokko

Tokko and friend

Tokko (特公) is a Japanese Manga series directed by Masashi Abe and written/illustrated by Tohru Fujisawa.
After the Machida massacre was found to have been the work of demons and mad alchemists (the 'Box of Dirge'), police and authorities set up the Special Public Safety Task Force, (or Section 2/Tokko) to deal with said nasties. Think X Files but with more swords, beheadings and super cool ninjaesque moves.
Superintendent Ryoko Ibuki recruits survivors of the Machida massacre for Tokko (who all save one have tattoos which protect them from demons) and so begins what turns out to be a really cool Manga series with lots of nice slashy, stabby, stabby goings on. I won't reveal anymore of the story here because that would be Spoilerific but if you happen to be into X Files/Men In Black stuff there is a good chance you'll enjoy Tokko. I certainly did. And when its on Play.com for a mere £3.85p (well it was before Christmas) it would be silly to ignore.