@NARKist so here's the thing.
Nea may be a cute girl, but she's not really human at all. I think there's some blue and orange morality going on with her. Her father kept the humans as a blood bank and her mother toyed with their corpses. She really thought she was doing the right thing with what she did - despite it being evil by the readers' standards (mainly because she was lonely). She realized after her defeat that she actually was evil and wanted to die - before deciding to become MC's familiar, which in her mind was "okay, you want me to live so bad, then you take responsibility". So yeah, she did some terrible things, but she's actually fully capable of a legit face turn.