Master of Arms is one of two secret jobs in Octopath Traveler 2 which requires you to collect items to unlock the skills. In particular, you will have to grab rusty weapons which a blacksmith will forge for you. This secret job is a must get as you are awesome against Hikari and anyone you want to hit really hard for a lot of damage.
These weapons must be equipped with your weapon master so that they can make use of the respective ability. For example, if you don’t have the Dancer’s Blade, you can’t use the dagger ability.
Most of these weapons just hang in chests, but a few are protected by big boss enemies that you have to defeat to get the weapon. If there’s a dungeon that isn’t used in the game’s story, it probably has a rusty weapon, guarded by a boss.
Like the inventor items, you also need a character that can take items from NPCs and a character that can take out NPCs to get all items. Again, we recommend Agnea and Throne.
Below we highlight where to find the boss’s rusty weapons and any related weaknesses.
Rusty Sword (Sword of the Conqueror) location
First you need one Sturdy pickaxe of a former miner in Orerush. You can find them in the gun shop:
Image: Julia Lee/Polygoon | Source images: Square Enix
After you get the pickaxe, go to Winterbloom and help this woman get the Rusty sword from the stone.

Image: Julia Lee/Polygoon | Source images: Square Enix
Rusty Polearm (Warlord’s Spear) location
In the western part of the Timerain Castle Town Square, a man will block a door. Knock him down as you please and enter the room behind him. There will be a path to the east that will lead you to a chest with the Rusty pole arm.

Image: Julia Lee/Polygoon | Source images: Square Enix
Rusty Dagger (Dancer’s Blade) location
The Rusty dagger is located on the Empress shipwreck, which you need the boat for. (If you haven’t unlocked the boat yet, you’ll need to do part of Partitio’s trading story first.)
The chest with the dagger is just in the captain’s room of this scary ship.

Image: Julia Lee/Polygoon | Source images: Square Enix
Rusty Ax (Lionheart’s Axe) location
The box with the Rusty axe is clearly visible in Quicksand Gaol’s dungeon, but you’ll be warned if you get too close to an ominous presence.
The boss, Lord of the Sands, is not much of a problem to remove. It is weak for sword, dagger, axe, ice, And holy. It will sometimes gobble up one of your teammates, leaving them with nothing to do, so make sure you’re ready before you take it on.

Image: Julia Lee/Polygoon | Source images: Square Enix
Rusty Bow (hunter’s bow) location
The Rusty bow is in the deepest part of the Sinking Ruins, guarded by the boss colossal.
Again, if you get close to the chest, you’ll be warned that there’s a boss ahead of you.
Behemoth can be tricky because it will petrify Your teammates. You can either use a healing item on it (herbal potion) to heal the petrification or you can use an accessory (divine necklace) that prevents this. Behemoth is weak for it polearm, axe, bow, And ice.

Image: Julia Lee/Polygoon | Source images: Square Enix
Rusty Staff (Spirit Lord’s Staff) location
The Rusty Staff is in the center of the Seat of the Water Sprite, which you can reach by passing under the waterfall in Borderfall.

Image: Julia Lee/Polygoon | Source images: Square Enix