Chiaki, a compassionate yet solitary teenager, is the hybrid child of a mortal woman and the Archangel Michael. Her celestial lineage, however, has caused Chiaki to be shunned by her heavenly peers. Nevertheless, her fate takes a turn when she takes in Ororon, a forlorn devil who pledges to be her eternal companion.
Although Ororon is the youngest son of the Lord Devil, presenting a major threat to his elder siblings' rule, he has also been banished from his domain. As both heaven and hell persistently endanger their lives, Chiaki and Ororon realize the potency of their bond.
As they embark on their odyssey, they learn important lessons from one another. Chiaki discovers how Ororon's formidable might can assist her in combatting the messengers of heaven. On the other hand, Ororon learns about the value of life from Chiaki, especially when an army of assassins are sent to eliminate him.
