The Brave Man Who Lives with the Proud Demon King

The Protagonist Is the Butler, Elegance, and Black Butler.

White-haired butler, handsome, elegant and noble.

Sir, You Can Be a Hero, but I Can Only Be a Devil.

In Another World, the Heroine Is a Hero and the Hero Is a Devil.

In the medieval magic world setting in Japanese anime, the heroine hates the hero at first but then likes it little by little.

There Was a Gender-Transformation Novel Before. I Turned into a Demon King and Was Captured by a Brave Man. Please Give Me the Title of the Book.

I want to read a book like "Her Royal Highness Wants to Kill the Demon King Today".