Tenraku Akuma! Demon's Core

A recently defeated demon crashes through the ceiling into the path of an exorcist, but she is not the menacing, alluring creature he had just fought. Lacking horns, dressed in tattered clothing, and clearly in need of food, she claims to be there for his soul, though she appears harmless. Rather than destroy her, the exorcist feels compassion and buys her food. She becomes determined to accompany him, hoping to prove her worth by helping in any way she can.