In the game's story, Kevin is a cyborg cop in the year 2010 AD in service of the Galaxy Police (Grave Crimes division), codenamed Type Valentine MX-5 (MX-5 for short). Armed with an energy bullet, his mission is to eradicate out-of-control parasites and their mutated hosts, gather their power, and proceed through to the next world.
Feeling pain every time he gets hurt (something he shouldn't feel as a cyborg) and that "something is crawling around inside of him", he finds out ultimately that he is one of the parasites himself. Dr. Jose, who was one of the researchers behind the parasites, had created Kevin in order to use him as a weapon to control the universe, leading him along this path to gain more and more power. Refusing to be used in such a manner, he fights against the doctor, and then is left to ponder his fate.
At the end of the game, he receives a message from headquarters, telling him Earth is being overrun by terrorist cyborgs. Debating the matter in his mind for a moment, he chooses to continue fighting, and returns to Earth.