The Man in Black was desperately looking for a cure for his sisters terminal illness. What made his situation unique is that he was linked to her not only by blood but by their own super powers. They shared a ‘Dual Intangibility’ which means that only one of them can exist in full physical form at a time. Should his sister die, the Man in Black had no idea what would become of him.
They both attempted to do good with their extraordinary power, fighting crime at a low level with some success before the sister became ill. Red Mist had noticed their crime fighting efforts and offered a potential way to help them. The Man in Black was very keen to do whatever it took to make his sister better.
Dual Intangibility gives both brother and sister a sizable advantage in any fight as it is not simply a 2 versus 1 situation but also an opportunity to pick and choose when and where to get their moves in by working together.