Hatsune Miku - Weekly Shonen Bye-Bye (週刊少年バイバイ)

Everything ends; a key point is when.

This song is in reference to Weekly Shonen Jump, a popular magazine containing many serialized manga. So the "jan!"s in the chorus are meant to sound like "jump!"

Original video: www.nicovideo.jp/watch/sm19028880
Lyrics: vgperson.com/lyrics.php?song=shonenbyebye