The first time I thought the new girl wasn't really a demon and instead just a very chuuni average girl and Tapiz made a wrong assumption because of her gloomy aura... But then she comes with a freaking longinus lance and minions and I was like "OH OK!!" lol
That's what I thought. It's too bad it wasn't intentional: it would've been fun seeing Tapiz realize that she's just an out-there human just in time to be proven wrong.
Based on the picture from volume 6. I think Kurona is a demon/angel hybrid. The picture shows her at a crossroad. Angel is one direction, demon on another, and her emblem is right in the middle facing another direction. This is just a theory though.