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