"So there's this fic I've been looking for and I can't find it. It's based off Harley Quinn and The Joker and it's on ao3 I know that. Dan was crazy and had voices in his head and he talked to them a lot and it was only a couple chapters in when my phone died. And Phil was kind of a serial killer and they met at a robbery?? Sorry this is so vague fuck" This actually sounds more lik Neon Homicide by Analphancones
Dan, better known as Danny Boy, is London’s top thief. He steals what he wants whenever he wants. Phil, better known as Sadiso, is London’s most wanted killer and thief. Him and Dan have been in competition for top spot on London’s crime charts, until one night they happen to meet.
Slowly, they start to come to grips with the fact they’re equal. Phil thinks he can use Dan though, and as he tries to break him, he winds up falling for him.
Dan thinks him and Phil will go their separate ways eventually, but as he falls harder and harder for him, he realizes that won’t happen.
They both struggle together to live a life of crime and not be caught, to hunt and kill, to prey and steal, without being found. They both live on the run, together now. Through struggles of not understanding love, through feelings they had both never known before, sex and homicide, love and lies, and crimes and kisses, they stick together.