Tenshi Akuma Kouhosei

A newly born supernatural (angel/devil) girl is raised in the care of Keith the Angel and Rivelle the Demon.
Each day one of them is able to teach a lesson in good or evil.
After 7 days the newborn will inherit the properties of one species or the other.
Will Keith persuade her to the army of heaven? Will Rivelle convince her to side with his world?

[From DLsite English]