Once upon a time, there was a multiversal war. It was between the forces of (a) Hell on one side, and several goddesses and their allies on the other. 

The goddess-backed company won; and so the hell was conquered and made just another part of their trade empire. Slavery and nonconsensual torture were abolished, which made a lot of the lower ranks of the demons very happy because they were the ones being tortured and enslaved. The hell recieved a new name: Cthonia, the under-earth world. The magic of the jailer-demons who could enslave with a name was outlawed and suppressed. 

Some years after the conquest, a pair of lower-ranked demons, husband and wife, moved to another world in the goddesses' empire. This world was called Arcbright, and it was a paradise unlike any they had previously known. The customs here were strange, but better; and so they tried their best to raise their daughter in the Arcbright way.