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PA Fragment
From The re-PSUPedia
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.
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.