It looks like a toy but it is not. This YoYoFactory Hubstack Afterglow...
Super tough Poly/ Kevlar Yo-Yo Strings! The toughest strings ever! Each pack contains 10 Yo-Yo strings.
Glow in the dark Kevlar Yo-Yo Strings! The toughest strings ever, now glow in the dark!Each pack contains 10 glow in the dark Kevlar strings.