The Tiniest Reaper just isn't very good at his job, the reaping of things small and smaller, just yet. He tries to look all tough with his hoodie jumper and ripped off sleeves. But, really, he's not tough at all. The worst he can do to you is to give you dead arm or dead leg for a bit, that's about it.
He's trying though! With a little practice, and a lot of growing, he may one day be full reaper.
(Unlikely, but don't tell the poor dear little reaper that.)