happy birthday (artist), hatsune miku, vocaloid, 00s, 1girl, 2007, :p, ahoge, aqua hair, arm up, back, black skirt, blue background, collared shirt, detached sleeves, female focus, from above, from behind, grey shirt, hair ornament, happy birthday, headphones, headset, long hair, looking at viewer, microphone, miniskirt, necktie, pleated skirt, shirt, simple background, skirt, solo, speech bubble, striped background, tattoo, thought bubble, tongue, tongue out, twintails, upper body, upside-down