Kung Fu Love/WMG

Hanako didn't do anything to become the Enemy of the World.
(Except, given her personality, possibly volunteer for the position if it wasn't randomly selected.) The whole Enemy of the World thing is a term of the peace treaty that was mentioned immediately before it was announced; the treaty created world peace on the condition that a single person is chosen to be the scapegoat for every bad thing that happens. Instead of countries going to war against each other, everyone goes to war against her. Presumably if one country has a real grievance against another wrapped up in "This happened because Hanako did such-and-such!" and a member of their military manages to kill her the other country would need to bow to fixing whatever "Hanako" did then work twice as hard to kill whomever becomes the next Enemy of the World to get back whatever they needed to give up.

To anyone who's read/viewed Kino's Journey it's similar to the setup in the Peaceful Land; the one which is only "at peace" because two countries which had been at war for 200 years switched to slaughtering the helpless bystanders living between them each day and chalking up a win to whichever side kills the most without their own people ever being in danger.