hajimete no oto (vocaloid)
English: The First Melody
A Vocaloid song by malo featuring Hatsune Miku and one of the earliest Vocaloid songs to gain popularity. The song name (初めての音 in kanji) is a pun on Miku's surname. A sequel song was later released: Mirai no Uta (Once again a pun on Miku's name).
NicoNico: https://www.nicovideo.jp/watch/sm1274898