The Silken Shirt is a mystic armor in Final Fantasy XII that boosts the wearer's Defense by 6 and Magick Power by 2, and in the Zodiac versions, MP by 8. It is the third weakest mystic armor in the game.
In the original PlayStation 2 version, the Silken Shirt is sold for 300 gil in Barheim Passage before obtaining the Treaty-Blade, Rabanastre after leaving Barheim Passage, Dalmasca Westersand after the Leviathan but before obtaining the Treaty-Blade, Nalbina Fortress, Bhujerba, and Dreadnought Leviathan. It is also rarely stolen from the low level Ghost during the storyline-mandated trek through the Garamsythe Waterway.
The Silken Shirt is sold for 300 gil in Barheim Passage, and afterward also in Rabanastre and Nalbina Fortress. It is found as a treasure in Garamsythe Waterway's flooded No. 10 Channel (70% chance to appear, 40% chance for gil, 50% chance the item treasure is the Silken Shirt without the Diamond Armlet equipped), and Nalbina Dungeons' The Black Watch (80% chance to appear, 30% chance for gil, 50% chance the item treasure is the Silken Shirt without the Diamond Armlet equipped), as well as in the Trial Mode Stage 5 with the Diamond Armlet equipped. It is still rarely stolen from the low level Ghost during the storyline part of Garamsythe Waterway.
The Silken Shirt is the third weakest mystic armor, giving 6 Defense and 2 Magick Power, as well as 8 MP in the Zodiac versions. Mystic armor offer magick-related bonuses that affect all types of magickal actions, from casting black magick to damage an enemy, to casting white magick to heal the party. Magick Power is also a factor when determining damage dealt by katana, staves, and maces.
In the Zodiac versions, White Mage, Red Battlemage, Black Mage, and Bushi can equip it. If the player starts Vaan, Balthier or Fran in any of the aforementioned jobs, the Silken Shirt can be worthwhile. In the original version, party members can wear any equipment piece and the HP-boosting light armor and Strength-boosting heavy armor are likely better suited in this early point over mystic armor.
The shirt can be rarely stolen from the Ghosts in the Garamsythe Waterway during the time Vaan, Balthier and Fran navigate through it on their escape from the Royal Palace of Rabanastre; Vaan starts with Steal, and so it is potentially available at this point. In The Zodiac Age version, the player can also try their hand at the Trial Mode at any time and bring the spoils to the main game, and so they could reach Stage 5 to open the treasure there with the Diamond Armlet (itself a treasure in Stage 1) with just Vaan, or possibly with Vaan and Penelo when she joins in the early game, allowing the player to skip purchasing the preceding Light Woven Shirt.