So, Saga of Soul/X-COM crossover.
I'd actually written that one a while ago, on the SpaceBattles forum (and, today, have uploaded it to fanfiction.net).
Now, this is a crossover, and it helps to be familiar with both source materials. I hope everyone can enjoy it regardless. It is, of course, completely non-canon (though the X-COM games are often on my mind when I write this story, as mentioned in the author's notes).