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PA Fragment
PA Fragments are given as a reward for completing free missions and receiving a rank of 'S,' along with the traditional meseta and mission points/class experience. These items cannot be, bought, sold, or traded to other players as of yet. However, one can transfer them from his or her own character to another character on the same account through the player's shared bank. No information regarding this has been released, so for the foreseeable future, they will remained bound to players' respective accounts.
While the description reads:
"Becomes a target for enemies and defends allies for a set amount of time," these items are used to purchase "Ultimate" Photon Arts in a quest which has yet to be released on the PSU US servers. These Ultimate Photon Arts are not purchasable from NPC shops, nor are they purchasable from Player Shops.
It is unclear at the moment whether there will be any other use for PA Fragments in the future.
The maximum number of PA Fragments a player can hold on their character at a given time is 99. As mentioned above, these items can be stored in players' shared banks, and in the player's Partner Machinery bank.