The few times that the child's dreamscape was investigated were disastrous. One angel and one Soldier of Dreams were killed when they tried to reach the boy. The angel managed to report that an entity known as Mr. Black was guarding the boy and using the dreamscape as an effective weapon. The players are sent to free Sean from Mr. Black's influence.
The going will be quite rough. The dreamscape is difficult to navigate and the players face creatures drawn up from a boy's nightmares. And in the center of all of this is Mr. Black itself. He will not let anyone come close to the boy and will defend him ferociously.
Mr. Black is an Ethereal Spirit that was formed by a random collection of forces. He stumbled upon Sean's dreamscape by chance and began to talk to him. He was shocked to the core of his being at the idea that the boy's parents could be so brutal and he encouraged him to spend more and more time in the Marches. Sean began to rely on Mr. Black's company and withdrew from a world that was too terrible to stay in.
The ethereal is completely unaware of the harm he is doing to Sean. He simply wants the boy to heal from what has been done to him. If the angels can show what is happening to Sean, he will help as best he can. Otherwise, Sean will stay longer times asleep until he simply slips away from the world altogether.