Killing for Affection
A character is in love with a killer, and starts kills others, thinking that the killer approves/will fall in love with them
Here's a rough example: a mentally unstable woman has heard stories of an assassin who's the best at what he does. Thinking that all he cares about is killing, she becomes a murderer herself. She commits violent atrocities with the expectation that the assassin will be so awestruck by her actions that he will seek her out, and they'll be together forever. Even though she goes so far that she's eventually given a nickname, the assassin never actually notices. This pushes her further and further over the edge until she's finally dealt with by the authorities.
Hello, Unknown Troper. You'll need to get known to lend a hand here.