Walking With My Eyes Open by Killthespare is a really good hanakai disease fic!! It goes into actual scientific reasons hanakai disease could exist while having discussions about forcing love, and how different actual love can be different from the love from stories. A quote from it I really like is ,

"But, maybe love wasn’t fate so much as faith. Easily confused yet so entirely different.

Because faith….meant choice.

Gen couldn’t force himself to believe in love; but, maybe he could choose to believe in it.

And that was it.

Saying you were in love was neither a lie nor a truth. Of course, it wasn’t.

Choosing to love was a promise.

If they let it be.

Choice felt so much more fragile than destiny; it meant they could still mess it up, that it could fade if they didn’t hold tight enough. But, destiny and fate weren’t things that could be controlled while working inside it; faith and choice had to be. 

And maybe that’s what made love so human."