Den is currently a very mysterious character.
All that is known so far is that she knowns Robin, and she seems to have control of an immensely powerful machine related to a fake moon. She seems to be capable of reversing a "Class 2 timestop" with absolutely no effort shown on her part.
She is an irritable individual who makes her residence in what appears to be an abandoned theater. She seems to enjoy reading. She also seems to be annoyed by Robin, though she still follows his orders.