Taimanin!

From the introduction: This is a world of darkness. Where once there were rules of non-interference between humans and demons in ancient times. But now through the evil and greed that rests in human hearts those rules have been eroded and criminals consort with the forces of darkness. Demons can now walk openly among humans and civilization’s morals are being corrupted. However not all is lost as there are those who still walk the path of righteousness. In Japan those are the forces of the Taimanin, a government backed group of anti-demon ninjas.