Armamentalist is an advanced vocation in IX, and is essentially a combination of a mage and warrior. Their function is to buff the team (mainly using Oomph) and debuff the enemy. An armamentalist can wield wands, bows, swords and shields, while also being able to weaken enemies with a variety of status effects (they only learn two buffs). None of their spells deal direct damage to enemies (unlike the mage, sage and priest) and they possess average defenses. One of their main selling points is the fashionable class outfits they receive. They have more MP than the warrior and gladiator combined and are also faster than both, meaning if you want to play a decently strong class with enough MP to use a lot of spells and abilities, the armamentalist is a great choice. With the proper skill sets learned from other jobs they become great all rounders, although this applies to most classes. Their Coup-de-Grace, "Voice of Experience," which increases the EXP payout after battle by a random multiplier (x1.1 - x1.9) is among the most useful Coup-de-Graces in the game.
The armamentalist's class-unique skill is the Fource. The Fource skill tree provides bonuses to health, defense, strength, charm and attack. You will also unlock different elemental Fources, (e.g. Fire Fource) that the armamentalist can imbue themselves or other party members with, raising their attack and defense as well as allowing them to deal damage based on the used element of the Fource, which is very helpful for dealing with legacy bosses. Multiple can be used on a character at a time, and if the level 40 class quest for the armamentalist is completed, the player receives an item that allows all party members to gain the effects of a selected Fource.
Windy at Alltrades Abbey says you must use the Fource of Mother Nature if you want to join the great fellowship of armamentalists. He wants you to erect a Wizard Ward before defeating two metal slimes in battle.
Hint for solution
Equip your mage party member with Poison needle, and weaken the slime with a Metal Slash, a sword skill, after you have casted Wizard Ward.
Adds fire element to target (self or ally).
Natural Strength +10
Permanently adds 10 to strength.
Adds ice element to target (self or ally).
Natural Resilience +20
Permanently adds 20 to defence.
Adds wind and lightning elements to target (self or ally).
Natural Charm +10
Permanently adds 10 to Charm.
Adds earth and darkness elements to target (self or ally).
Functionally the Armamentalist is identical to the Red Mage Job Class from the Final Fantasy series, being able to equip swords and shields and use magic at the cost of below average stats. The artwork of the male Armamentalist from IX even wears an outfit very similar to the standard Red Mage outfit. You also need to complete a quest in order to unlock the the armamentalist, like the Red Mage.
The coats of armamentalists from IX as well as the rapiers seen in the official artwork resemble 17th, 18th, and 19th century military fashion. The outfits likely contribute a lot to their popularity as a class.
The name armamentalist is a play on the words armament, meaning weapon, and mentalist, describing a sort of magician. It also sounds similar to the word elemental, referencing their use of the elements in their magic.