So most of us 팬 know the song, "Disappearance of Hatsune Miku," right? Well, it wasn't just wrote for nothing. Read 더 많이 if 당신 want to find out about the story.
A few weeks after Miku was released, her fame had grown to such a large scale that millions of people kept searching "Hatsune Miku" on Yahoo! and Google.
Yahoo! and 구글 thought that Miku was spam. So when a person would 검색 'Hatsune Miku,' it would lead them to no where. Which, in other words, means that 당신 would not be able to 검색 'Hatsune Miku' on Yahoo!, 구글 또는 YouTube.
The 팬 went crazy nuts, and so the song, "The Disappearance of Hatsune Miku" was created. Seeing the fans' rage because of their action, Yahoo!, 구글 and YouTube brought back Miku and apologized.
And so, that is why we celebrate 'Disappearance Day' every October. (I don't know the exact date)