Royal Rank is a special feature where you can acquire a variety of different benefits.
You can get Royal Points to help increase your rank by purchasing Visiore or completing Missions.
Increasing your Royal Rank allows you to unlock the Speed-Up function and acquire various benefits such as increased JP acquisition from the Barracks.
*For more information on what benefits come with each Royal Rank, check the Royal button on the Visiore Purchase screen.
Additionally, the day after you have gone up to Rank 1, each day you can receive a Login Bonus relative to your rank as part of your Daily Mission rewards just by logging in each day.