In the world of Black/Matrix the forces of Hell won a decisive war against the forces of Heaven. The victorious devils rewrote history and redesigned society to suit their purposes, reversing the concepts of good and evil. The descendants of the devils, known as black-wings because of the bat-like wings that grow from their backs, rule over the white-wing descendants of the angels, whom they treat as sub-human slaves. In their society love is considered the worst of crime, and any one found guilty of love or kindness is hunted and punished.
Black/Matrix + is the second remake of the original Black/Matrix and added additional content and improved the graphics.
Source: Wikipedia, "Black Matrix (video game series)", available under the CC-BY-SA License.