It was going to be a pain in the ass trying to get the sand out of his automail after all this, but Edward had decided that it would be worth it going with Mello though he didn't know Demyx, and he wasn't sure who else was going to be there. But that had never stopped him before when he wanted to go somewhere so he just prepared himself for the inevitable trouble of de-sanding his automail and grabbed himself a bathing suit from the closet despite that he wouldn't be doing much swimming.
When they finally got there, Edward was just as surprised to see what was going on even though he was plenty capable of doing it with alchemy. That wasn't alchemy, though, and even knowing that there were people in the building that could do those kinds of things without the help of alchemy was still surprising.
He was still watching the dancing water figures when Mello started walking again and he hurried to catch up, looking around for somewhere to spread out their towels. "Over here, okay?" he asked, nodding to a patch of sand.