I hope they encounter that angel Dou made a promise to in the past, which will set shit straight with catto.
That said... Dou being able to use magic raises several interesting possibilities. It's possible that she isn't a being that possesses demonic attributes, after all, and we've seen she hasnt a mean bone in her body. Her seeming 'soothing aura' also seems to be a result of her being an anathema to cruelty and aggression. Normally, that would be something a heavenly being could do.
Though the fact the cat angel and elephant both weren't effected by the aforementioned aura also raises several questions. We've seen that on 90% of demons, it works. Even in humans, the aura worked, though in general most humans encountered weren't super hostile to begin with. Yet both angels encountered in the story, and the heavenly beast, were either resistant or totally immune. Hell, she didnt immediately pacify the angel she befriended, either. She had to show her good heart and pure intentions to him before he chilled out. Hm...
Ah, I'm reading too much into this, since lore isnt something this manga seems to delve into, but it's fuel for my speculation.