Uniquely, he also has the opportunity to play the character within a kind of love story. That must give an actor a great deal on which to chew.
I don't think their is any real 'love' between Harley and Joker, even from Harley's side.
What Harley really feels for Joker, is Obsession.
And while obsession can sort of resemble love (why so many people confuse the two) ultimately it is self-destructive. When you are obsessed with a person or a thing, they become the center of your universe to the point where nothing else truly matters.
The best example to distinguish obsession from regular healthy love, is that obsession is like addiction...you might recognize it's bad for you, that it's destroying your life, but you can't give it up.
Harley views her relationship with the Joker as romantic, because she can't face the reality of what has happened to her. She lives in a fantasy world where the two of them are Bonnie and Clyde to avoid the cold hard truth that Joker destroyed her life. Joker recognizes this, and therefore he plays on Harley's fantasy to keep her attached to him so he can continue to use her for his own goals (hurting Batman). And so long as Harley lives in this fantasy, Mr. J can continue to use Harley as he sees fit.
That's how I always saw their relationship, and why I always found it rather fascinating despite how abusive it is. But I usually tend to avoid discussing Harley with other fans...because a lot of people tend to romanticize her relationship with Joker to the point where it seems some of them share Harley's 'fantasy' with her.
I really hope Ayer goes all out and shows their relationship for the truly screwed up look on obsession and mental illness that it really is. That's more fascinating to me then some silly Bonnie/Clyde romance.
Just my opinion of course.
