Idle thought for a story - a woman who can project her imaginings into the mind of another woman at night in the form of dreams.
I really like this, and I love both replies, but will throw my own idea in too, for good measure.
A man who can project his imaginings into the mind of two woman at night in the form of dreams. He makes both of them dream about catfighting each other, over him. Both dream that they lose and each tracks the other down to settle things irl.
They meet and end up rolling around furiously pulling each other's hair as the guy watches.