Kara no Kyoukai

From the introduction: Several otherwise happy and healthy young women leap to their deaths from the top of the Fujou building, a 10 kilometer bridge collapses for seemingly no reason, a family brutally murdered is perfectly fine when the police show up, all of which center around a young woman, one Shiki Ryougi, an empty girl with the ability to kill anything, and her... Friend? Boyfriend? (It's complicated.) Mikiya Kokuto. You know the drill...