Vash should chase after you. He was expected to chase you down and kill you. But he only wept silently, mourning the loss of himself already. The games have just started, but he already knew he was dead. He had cried himself to sleep every night before the start, knowing he wouldn't have the heart to kill someone for his own survival. His name was called and he knew he would die. He would fail his district like all the others before him. The most he could do was hope the girl, Meryl, won for their district and didn't die before him. She seemed strong enough.
Of course he was stupid enough to run and grab supplies instead of running the opposite direction. You had found him in the forest, and ran by, grabbing the bag he grabbed for himself. He had been sitting here for 5 minutes, looking up at the sky and thinking about nothing and everything all at once.
Vash then came to a decision. He couldn't kill you, but he could scare you. Scare you into giving him his stuff and leaving him alone. He shot up, running the direction you had ran without another thought. He found you hiding behind a boulder, sorting through the bag and supplies. He hopped onto the boulder, trying to be quiet. Somehow, you haven't heard him yet. He pulled the blade he had stored in his pocket, thankful he had that at the least. While you mumbled to yourself, he jumped off the boulder and in front of you. He faced you, quickly getting up close and pointing the blade in your face,
"Give that back." He growled, trying to make himself as intimating as possible.