Hatsune Miku - Take It Easy!!! (translated) 

Credits
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www.nicovideo.j...
Song: 今日犬 (Kyouinu) a.k.a. ジャムおじさんP (Jam Ojisan-P)
Vocals: 初音ミク (Hatsune Miku - Vocaloid)
Original title:
ゆっくりしていってね！！！ (Yukkuri Shiteitte ne!!!)
Notes
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The "Miku Miku Fairy Tale" title at the beginning is pronounced "Miku Miku Douwa." Sort of a pun off "Nico Nico Douga."
"Take it easy" is the popular translation of ゆっくりしていてね！ (yukkuri shiteite ne!). The phrase makes sense on its own in this song, but it's actually part of an odd Japanese internet trend that will take a little explanation.
First, there is a popular vertical-scrolling bullet hell series of shooter games referred to collectively as the Touhou Project. The characters in the game are a collection of girls who fight in the sky with magic spells and a cast of supporting characters. It's attracted a large following, in no small part because of their creator's permissive attitude toward derivative works. One fan group is even producing an anime series based on the Touhou games.
The "yukkuri" are another Touhou fan creation. A yukkuri is the exaggerated, disembodied head of a Touhou character. Their catchphrase is "Take it easy!" because that's what they do: very little. They originated from a failed attempt at recreating two main Touhou characters in Shift JIS art (the Japanese equivalent of ASCII art). Yukkuri have been a popular meme ever since.
The background image of this video is a yukkuri-styled Miku.
A Nico Nico Douga animator named Piroshiki+ created a video for this song:
• Hatsune Miku - Take It...
Video description translation
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I wanted to take it easy, you know
Even though it's bad, it can't be that bad, right