So most of us 粉丝 know the song, "Disappearance of Hatsune Miku," right? Well, it wasn't just wrote for nothing. Read 更多 if 你 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 谷歌 thought that Miku was spam. So when a person would 搜索 'Hatsune Miku,' it would lead them to no where. Which, in other words, means that 你 would not be able to 搜索 'Hatsune Miku' on Yahoo!, 谷歌 或者 YouTube.
The 粉丝 went crazy nuts, and so the song, "The Disappearance of Hatsune Miku" was created. Seeing the fans' rage because of their action, Yahoo!, 谷歌 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)