My guess, Hina had to deal with some fucked up shit at home that made her the way she is now.
There was an old photo of her, where she doesn't have this creepy smile.
The "domestic violence" joke.
And how she was on the streets during the night.
Look at the blood on her hands....Why she returned at human without eat? And .... they will eat dad's arm? Wtf, I need more about these 2 monsters!!!