In the beginning the two where in two different worlds Orie Soriyu was a angel. Her dad was Athena's (is god) war commander. She was next in line but someone will make that hold off. Down in Hell Hideki Gremory was a demon. His dad was Hades (is devil) war commander and like Orie he was in line to become war commander. The angels and demons were at peace and they where best friends even though they were super different they spent everyday with eachother.