Onnamao-sama ha Yuusha-kun wo Taosenai.

Onnamao-sama ha Yuusha-kun wo Taosenai. summary: Demon Lord Abyss was worried... about not being 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' true identity, considers her his "master" and becomes very fond of her...!