Manga where the demon lord leaves his daughter in charge who tries to save the hero

Question

So it's like where the hero comes to kill the demon lord but he left a note saying he left his daughter in charge. Later it's revealed the daughter is the demon lord and she's trying to save the hero because the crown the humans gave him is infecting his brain

Answer 1

Is this At the Demon King's Castle...?

The Hero has finally entered the Demon King's castle to begin the final face-off between mankind and demons. At the throne room, he was met with...

The Hero arrives at the Demon Lord's castle to confront him, but finds his young daughter sitting on the throne with a note from her father, stating that he had some business to deal with and left his daughter to look after the castle. Since she doesn't appear threatening, the Hero decides not to attack her.

It's later revealed that the daughter is the new Demon Lord, but she want to save the Hero from the crown given to him by the human king, that was designed to tamper with his brain and heart.