Nena's siblings were killed in the world she's from. Both before her eyes. She was going to die too but some guy rescued her. She vowed to kill anyone related to their deaths.

But this town isn't all bad! I met you, and Nena loves you because you're Nena's sibling! Nena will never ever ever ever ever let anyone hurt you! If they do....

[ Tight, tight, hugging ]

She'll do anything you ask!