Nobody's Fool (Harley Quinn! Dean and Joker! Cas) ~ Supernatural Destiel

Dean Winchester, a previous psychiatrist and current genius, now resides in a moldy apartment, eating scraps from the complex's trash bins. He struggled in life, ridden with anxiety and a life-ruining dependent personality, topped with post traumatic stress disorder. It took years to get over the abuse his father put him through, and he almost did, until Castiel Novak came in.

Castiel Novak, a permanent smirk due to the abuse of his father (and mother, and stepmother, but the scar was all his father's doing) scarred on his face, became villainous after his father died. He started killing when he became older. He never fell in love - he's incapable of having feelings other than sexual. Yet, he decides that Dean Winchester deserved his attention. Maybe, just maybe, since Dean was a psychiatrist, they could break through the wall of Castiel's mind. Or maybe... Cas can break Dean's, and they can rule the town of Lawrence.

(I know that there are many plots following mine, and I hope that the similarities do not cause trouble. I have not read any Harley Quinn/Joker Supernatural fanfiction, and therefore am not trying to copy.)