When a bio-terrorist’s engineered plague infects a superhero, he breaks out of prison to create a cure for the woman he loves.

>>?"it turns out to be the only way to kill a superhero"
It's not the only way, it's just that a villain who modified it modified is specifically so the superhero's known abilities wouldn't be able to counter it. (the plague itself wasn't meant to be a plague, and in fact plague is the wrong word but I didn't know exactly what it was when I started.)
But yes, the thing she created is the thing that is killing the man she loves. The concept is simpler than what people seem to be taking it for, but that's because I included 'superhero'.

So the central conceit of the story, the inciting incident, is an irony, that a woman bioengineers a plague (for whatever reason) ?that has an unintended consequence: it turns out to be the only way to kill a superhero, her ex-boyfriend, the man she still loves?

So the central conceit of the story, the inciting incident, is an irony, that a woman bioengineers a plague (for whatever reason) ?that has an unintended consequence: it turns out to be the only way to kill a superhero, her ex-boyfriend, the man she still loves?