This is a little like the Joker/Harley theme, but not really. Bellatrix is obviously the infamous criminal and Hermione is the young and naive soul healer. It takes place in Azkaban where Bellatrix is locked up.

"Ugh, so clingy!" Bellatrix complained, but it had no bite. As a matter of fact, she hugged the young woman back just as tightly. "Shut up! I watched you die, I'm entitled to be clingy," Hermione replied and nuzzled into the crook of her neck, inhaling the well-known scent.

Hermione is a special agent that's supposed to take famous criminal Bellatrix down. Magic is only very mildly touched, it mostly doesn't exist anymore.

Bellatrix is a pretty ancient vampire and Hermione is her 'meant-to-be'. There's no stronger bond that that.

Just plain filth...