The ironic thing about Hannah was that Dexter initially planned to kill her. Hannah murdered several people, including her husband and a counselor who sexually assaulted her. After learning of Hannah's crimes, Dexter managed to get Hannah onto his kill table. However, Hannah surprised him by telling Dexter to go ahead and kill her. Dexter then slept with Hannah instead.

In many ways, Hannah has her own code to justify her kills, just like Dexter. While Dexter only kills those who have murdered others, Hannah kills to survive. Dexter and Hannah's relationship doesn't change the couple's tendency to murder. However, there's never any doubt that Hannah and Dexter do genuinely love each other. In the Season 8 Dexter finale, Dexter left Harrison with Hannah (as a hurricane was approaching Florida and his sister was dying).