Scratch that, my story sucks. I'm typing a new one now on a text doc.
I'll upload it soon.
Ok here it is:
I always imagined Rivaldi to be the head of the Church's Intelligence gathering agencies. The Scorpion Tail being one of the benefits of that position. Though the only flaw I can see in your story is the "Shinto" as far as we're aware there is no Shinto religion in FFT. By FFT's time the only religion to have survived in Ivalice is the Glabados Faith. Now we do know that there is a land far to the East where the Samurai skills descend from so their teachings may be more accustomed to the Shinto religion, just wouldn't be called that, likely.
Thanks LD. I'll change the name to Araigo.