The story behind Dark Sector follows a character named Haden, an assassin employed by an American government agency to investigate strange happenings in the Balkin state of Lasria.
When starting the game you find that Dark Sector is codename for the bioengineered expieriments happening at Lotus Complex in Lasria. Basically, the projects go bad and a virus breaks out turning humans and animals into monsters. The infected organisms quickly transform into partially metallic lifeforms and are driven mad by the pain caused from the transformation.
Haden is intrested due to the fact that he is a killing machine who is sent in to investage the virus but while there is infected. However, instead of turing crazy, Haden finds himself in control of the virus forming a genetic defect called Familial Dysautonmia, which disables him to feel pain.
Sinclair stated, "You always have to have some kind of wierd superhero quirk."
To continue, Haden throughout the game will learn new ablities with his ever progressing infection including an ability you start with from the begining of the game called the "mag disc". The disc is a weapon you are equiped with from the begining; a 3-bladed throwing weapon that forms from the hand. You will use this "mag disc" to dismember enemies, grab distant objects, and much more. Sinclair joked by stating, "If we f--- this up, then we've lost everything."
Other than the disc, Haden will have powers and guns at his disposal. One of the things Sinclair touched base on was the fact that the animations in Dark Sector will be more realistic- in terms of using the weapons. For example: Haden will be hestitant at first when using the disc but as the game progresses and you use the weapon more, your attacks and animations will be faster and more fluid. Also, as the game unfolds you will fight many bosses where once you defeat them you will earn new abilities. One of them being the ability to create shields on the go using your disc to fan out and block any oncoming attacks.