I think that much of the appeal of Hannigram is in the fact that they are literally impossible, yet a perfect match at the same time. They fall into multiple tropes of doomed lovers/lovers who can't be/forbidden relationship, which makes them a very exciting pair that never bores. Serial killer/FBI agent, Doctor/Patient, Old money/Poor upbringing, Social butterfly/Misanthrope, Refined and classy foreigner/Down-to-earth American fisherman, Devil/Fallen angel, Narcissist/Hyper-empath.... They contradict each other in so many ways, yet they are mirror reflections of each other. Two sides of the same coin. For all the ways these two men can't be, something they have in common evens it out. Despite of who they are they think alike, feel alike, act alike, they can assume each other's point of view, they have similar interests, develop the same desires and the same ulterior motive. Both Hannibal and Will suffer from the same loneliness before they meet each other, and then suddenly there is someone who undoes that loneliness the way nobody else has before, and they are tied. They cannot let each other go after that. As Bedelia said it: ''Can't live him, can't live without him, is that what this is?''
For Hannibal and Will, there is all these ways and reasons why they cannot be together. Be it who they are, what they did to each other or what the world around them thinks, they cannot be. But they can't let each other go, because there is no one else on earth with whom they can be truly, unconditionally themselves: their beastlike, violent yet caring selves as they are.
It's what gives them their timeless appeal. Who among us doesn't want understanding and acceptance?
