The Royal Arms are special weapons that only Noctis can wield that are relics of ancient kings of Lucis. There's a total of thirteen you can acquire throughout the game, although you will get seven of them during the main story. That means the other six Royal Arms are completely optional and most of those will require you to trek through dungeons in order to reach them.
Story-Related Royal Arms
Royal Arm
When
Sword of the Wise
Chapter 2
Axe of the Conqueror
Chapter 2
Swords of the Wanderer
Chapter 3
Blade of the Mystic
Chapter 4
Katana of the Warrior
Chapter 10
Trident of the Oracle
Chapter 12
Sword of the Father
Chapter 13
Optional Royal Arms
Royal Arm
Location
Shield of the Just
Found in Tomb of the Just, at Thommels Glade area.
Mace of the Fierce
Found at the top of the Rock of Ravatogh. Look for a path in the big area at the top (not the slide).
Scepter of the Pious
Found at the end of the Malmalam Thicket dungeon.
Star of the Rogue
Found at end of The Myrlwood dungeon, in the Vesperpool region.
Bow of the Clever
Found at the bottom of Balouve Mines. After defeating boss, climb stairs to ladder and look for crack in wall to reach Royal Tomb.
Greatsword of the Tall
Visit Tomb of the Tall in Fallgrove area to find note that weapon is missing and likely taken to Costlemark Tower. Complete the dungeon by defeating boss at the end to retrieve it.
