It's an adaptation of a manga series by Masakazu Katsura. As of now, there's a total of 17 volumes to the tankoubon and is still ongoing. Do note that the anime is of a mature genre with it's fair share of violence and gore.
The anime is not a faithful adaptation of the manga, and will only be 12 episodes long. (There's a lot to squeeze in....) Can't wait to see how that turns out. The anime is currently at episode 5, which is equivalent to around chapter
The story traces the origins of two rival heroes - Zetman, born with the ability to transform into a monstrous figure, with superhuman strength, and Kouga, heir to Amagi Corp - a wealthy technological empire, with his specially designed suits and weapons. They fight to protect mankind and destroy monstrous abominations known as Players. These Players were created by Amagi Corp, as an intent to create perfect artificial humans. However Players ended up becoming a hobby for rich men to bet on them, gambling as they were pitted against other monsters to fight. Players finally gained awareness and killed off everyone in sight and escaped.
Fans of the manga seem to hate the anime. I first saw the anime and then checked out the manga. I am undecided as I like both of them a lot - the artwork for the manga & anime is beautiful, the storyline is pretty good. Some parts got me bawling. (embarrassed) In fact I'm a bit pissed that there is no English version of Zetman manga (I think) as it's definitely worth adding to my collection.
Do check it out if you have the time to spare. ;)