The noise has effectively startled Aang. He rolls to his feet in one motion, bracing Hariti in his palm, and turns towards the noise. "Who's there?"

He's flushing already, knowing someone must have heard him talking, as he slowly approaches the noise. Once he sees who it is, he's still flushing, but at least he relaxes a little. "...Hi."

He has never really spoken to Vivi, but he's seen him around the school all the kids are forced to go to. It's not as if he's a complete stranger.