In short, Hatsune is the spokes-character and pre-set for a sophisticated software mouth (or vocaloid) that users can program to sing songs. Not being content with just lip synching a song, a fan has taken the weird yet strangely catchy 10th end credits (according to ANN website) from a kids anime show called Keroro Gunso and made it into a cg version with super deformed characters of hatsune's world, doing the shows choreographed dance. Also of course, hatsune is singing this version of the song.

you can find a side by side comparison of the dance at http://www.youtube.com/watch?v=hrUOovvwc54

Added to meme channel for the last few seconds of the clip...