Once the Veil Was Taken Off, All the Civil and Military Officials in the Court Knelt Down and Begged to Keep Me.

I'm Looking for a Book Where the Male Protagonist Is Tough at First, Then Strong, and Finally Yandere.

Are there any books where the male protagonist is tough in the beginning, then becomes strong-willed, and ends up being yandere? The ending must be he-like, preferably an ancient novel, but modern ones are also acceptable (only for romance, don't rate too low, and don't recommend books that have nothing to do with the title)