Luna is Harley Quinn's little sister. Harley Quinn got took to Arkham asylum. But Luna does now that so she goes looking for her sister. While looking for her sister , she went to Joker. And with that she starts falling in love. So if you want to find out what happens to Luna and The Joker just read Joker's Little Girl. {Sorry I had a better description but it deleted itself so yeah. Bye my little chickens. } - Liz