Onnamaou-sama wa Yuusha-kun o Taosenai

Story:

Demon Queen Abyss is worried… She's not able to defeat the Hero, considered the mortal enemy of the demons. This Hero is still an inexperienced young man—he should be easy to defeat! … However, the problem is that he, not knowing Abyss's true identity, considers her his “Master” and has become very fond of her…!?