There are so many things I love about this. Let's see whether I can list them all without sounding either incoherent or completely insane.
First up, there's Cloud most definitely not being a morning person. Particularly on his day off. His whole "someone else will deal with it" attitude is fun, too. Then there's Zack. Zack with wings. Zack with wings, horns, and a pair of Sephiroth's black leather pants tucked well into his boots (I don't care what anyone says, there's still a 3" height difference between the two of them).
Then there's the way Zack's adjusted to things - sort of "yeah, I got wings and horns; nobody knows what caused 'em, nobody knows whether they're going to go away at all; but hey, it's cool". Meanwhile, Sephiroth (as per the fic) is busy putting the fear of him into all within a ten mile radius, by way of venting his frustration about the whole business; the rest of SOLDIER are just a weenshy bit distracted by new appendages and other Weird Shit happening; and all the people who have just had the booster are off shambling about Midgar like Dawn of the Dead. But hey, it's cool, and Zack's got enough time to stop and deal with a just-woken-up Cloud.
Then there's Cloud's reaction to the Wings. It's like, okay, Zack's got wings. Fiiine. It's Zack, after all. I can cope with that. Running in circles, screaming and shouting can be done Later. First, I want to find out where the blip the rest of my squad got to. Oh, and have a look at Sephiroth's new tail. Among other things.
Cloud's single horn (unicorn?) is nice, too.
I second the question about whether there's any chance of a followup fic in this universe - maybe a chance to see the chaos in progress? How the merry hey hold on a minute would they manage to fix that one? Oh, and what does Shinra PR do about the whole business?
(Meanwhile, my SOLDIER admin OFC is busy getting on the phone to Supply and placing an order for at least another thousand pairs of baggy pants, and a lot of new shirts with slits for wings. As she puts it: "If I panicked every time something unusual happened around here, I'd never get anything done!")