I made a theory:
The song talk about bullying, right?
I think that Miku isn't like we see her in this video, but she think that she is like this cause everyone is making fun of her, so she imagine herself, ugly, full of bacteria, this is why everyone isn't near her, because they make fun of her so YEAH. But a kind girl came to her and touched her, and she became the victim, there is a part where Miku laugh, she is making fun of that girl, so she became the bully and became part of the bully group. BUT she returned, at the end, the victim, saying: "I am again all alone". Is that like this?
I have problems.