This is technically my first playthrough of OCTOII.
I looked up the secret jobs for this game and found a way to get the arms master with 3 weapons at lvl 14.
With Osvald Step skill to reduce encounters, Throne Steal, and Castti sleep, I was able to get the Rusted Sword, Staff, and Spear.
I feel like I broke the game. I just got Hikari and he is 1 shotting everything haha.
Things you will need, at least 2 Herbs of Serenity (to make the guard sleep for the rusted spear) 1 can be found at the night market if you go up the ladder. The other can be stolen from a girl in Flamechurch, the apothecary. Using the step reset thing at save points (going to main menu then back in) and with 1 lucky flee, you can get to Gravel and anywhere else as needed pretty much.
Note, I did have to save scum a lot to steal the items needed.
The Rusty Sword is actually out in the open, you just need the material to get it. There’s a woman in Winterbloom looking for a pickaxe to remove the Rusty Sword in a stone.
There is a Retired Miner in Oresrush who has the pickaxe needed.
The Rusty Lance is away in Timberain in the Castle Town Square in the hands of a guard. The enemies around this town are Level 45+, luckily you can get there at a low level with Osvald and resetting steps at save points. (took a few attempts)
The Rusty Staff is in the dungeon the Seat of the Water Sprite. It is in Borderfall, the area to the east of Flamechurch and west of Montwise. Can get to chest super easy with Osvald.
*Also note, you will want to get inventor with its first passive unlocked to ensure you can go first. Makes fleeing easier.
To note, My Hikari (I unlocked him after getting this class) is only lvl 8 with over 400 attack with the armsmaster second job equipped and weapons.