DRAGON QUEST III HD-2D Remake

After defeating Robbin' 'Ood, the King of Romaria will offer you his crown. Select yes and after the cutscenes, the achievement will unlock. It does not matter if you're playing as the male or female version of the main character.

To continue with the game, you can either reload a previous save or speak with the King in the monster arena and tell him you no longer wish to rule Romaria.