(General WTF Question): Who is Hatsune Miku and why does she have a coreogrphed dance involving leaks and Finnish polka music?

Sorry if the title of the question is a bit vague, I really don’t know how to ask this.

A while ago I found a strange area on Youtube where Japanese manga cartoons dance to Finnish polka music while holding vegetables.

I just want to know what is going on, and why is this so popular. There are 1000’s of videos of the same character “Hatsune Miku” dancing to various songs, and videos of people imitating them.

I was curious to see if anyone knows anything about this in general, how it started, what it is, what it means, why they do it, and anything else you know.

In case you have no idea what I am talking about here is a video of Hatsune Miku dancing to and singing some Finnish polka.