Two recs, one of which I posted already on bangonfic:
And Shut the Gates of Mercy on Mankind by sagdragon, good one-shot about Isaaru coming to grips with failure following the Via Purifico. Interesting post-game conversation with Yuna about mercy. K rated.
Foundations by Broken Visage, dark one-shot envisioning Zanarkand's despotic dynasty and the birth of Yu Yevon. This is one of those great pieces that brings to life a period about which we know almost nothing, defines a culture and characters with a few deft brushstrokes, and hints at a whole lot more backstory by allusions, the way Tolkien will casually drop in a reference to the "cats of Queen Beruthiel" and leave you going, "wait, wait, tell me more!" Rated K+.
This author looks skilled, and I suggest browsing further -- I haven't yet but intend to.