Cameron Nemo lived in a dimension without knowledge of substance until he met Elisa Cameron at a young age. Elisa was able to enter his world and showed him form and substance opening his world and life. Nemo took great care of Elisa and was her "imaginary" friend as a child.
For reasons unknown but perhaps due to his loneliness of Nemo wanted to control Elisa and keep her with him. He tries to make his dimension into a perfect place for Elisa filled with all her wants and desires. Elisa spent a lot of time with Nemo. She was able to do this because when she enters Nemo's world she disappears from the real world and then reappears instantaneously back in her world when she leaves his dimension. On a side note she can also reappear anywhere she wants that she is familiar with. She can not appear in a place she has never been.
As Elisa got older she joined the Furies and became the Ghost and also became less interested in Nemo's dimension. This really made Nemo jealous and he transformed his world into a nightmare filled with deamons, monsters and visions of Elisa's past. His world became so nightmarish that Ghost did not ever want to go there again. Focus and Mindgame (fellow Furies) made Ghost forget about Nemo's dimension and she forgot she had the power. This was one of the many mind-altering experience that were put upon ghost and wreaked her mind.