<_< I know what it stands for.
If you're talking about why people think the SHU is the one that Sora gets on his knees in front of, it's basically because it's implied. The trailer shows SHU appearing and then Sora on his knees before someone, so it makes sense to assume that it's the SHU. Besides, the guy standing in front of Sora in that pic looks a little too built to be Saix. Or not. I dunno.
If you're talking about why people think the SHU is the one that Sora gets on his knees in front of, it's basically because it's implied. The trailer shows SHU appearing and then Sora on his knees before someone, so it makes sense to assume that it's the SHU. Besides, the guy standing in front of Sora in that pic looks a little too built to be Saix. Or not. I dunno.