An anime made by Tatsunoko, the masters of anime in japan.
The plot revolves around a bishonen, Otoha, former yakuza member, who earns the power to become a Karas, a superpowered ninja covered by a black armor. This armor gives him powers to protect the city against the mikuras, machine demons created by the former Tokyo's protector, Ekou, a Karas who turned against the city.
Also, there's the Yurines, fairies who travel together with the Karas, giving them their powers.
It is a unique anime with 3D-celshaded scenes blending with traditional animation, splendid fight scenes - they actually fight, instead of shitty, pointless drama and angst, like in naruto and twilight books.
Karas is also a top-tier character in Wii's crossover fighter Tatsunoko vs. Capcom and has a fighting style similar to Strider Hiryu, focusing on speed and chain combos instead of damage.
Karas is one of the best anime ever created.
Also, I love to play with him in Tatsunoko vs. Capcom.