Weapons: Everything excluding non-Onion Knight Legendary Blacksmith items and summons
You heard right. The Onion Knight can use everything from your inventory—except what you might get from the Legendary Blacksmith designated for other jobs! The Onion Knight also can’t use summons, but they can use all other kinds of magic at all levels, with enough MP to throw around, unlike the Sage. The Onion Knight is literally the best job in the game, and this includes stat growths and caps. If you unlock the Onion Knight job, there is no reason to use any other job, and this is intentional, because this job has one huge condition: You must be at Job Lv.99 or your stats will be the worst out of all the jobs. Yes, the Onion Knight will only really show its true colors once you have achieved complete mastery! This is in line with the philosophy of the Onion Knight: achieving mastery and accomplishment through determination and a lot of hard work.
You most certainly don’t need four Job Level 99 Onion Knights to beat the main game, but for those looking to complete their characters and truly master the game, you can’t beat the path of the Onion Knight.