I found this @ Nexus as No 1 mod... http://www.tesnexus.com/downloads/file.php?id=30239
Can someone tell me what is this for?

It's a mod based off of Devil May Cry, complete with the four normal combat styles from DMC 3(or all of the games, I've only played 3), complete with a working gun(well, it's a animation in which you fire a gun, which works), even has Bullet Rain when you use Gunslinger mode(jump up in the air, double jump a few times, and hit the special button, and you aim to the ground and let loose a rain of bullets, which tends to hurt things bad).

It's one of those Japanese mods which are so friggin' awesome but completely lore smashing(as if anyone who uses the mod would really care about lore issues enough to complain about that).
Fun mod, but it takes a couple extra buttons then normal mods(hotkeys, need more hotkeys), and it's somewhat uninntuitive(I certainly didn't pick it up fast), but it's a fun mod despite it.

Oh, and it has a Devil Trigger mode. 'Nuff said.

Looks like it's been pulled from TESnexus. Think it violated any copyright laws? It had quite a bit of material that seemed to have been pulled right out of Devil May Cry. It no longer is in any rankings. And the link is dead.