むかしむかしのきょうのぼく (Mukashi Mukashi no Kyou no Boku) is a Vocaloid song by DECO*27, one of the most prolific producers in the Japanese Vocaloid scene. Originally released on DECO*27's 2010 album 愛迷エレジー (Aimei Elegy), the track features Hatsune Miku on vocals and was accompanied by an official music video directed by Yojizen-P with illustration by Hayashi Kentarou and animation by Poeyama. The title translates roughly to "Me of Once Upon a Time, Today," and the lyrics reflect on past sorrows, self-reflection, and the quiet determination to move forward, an introspective theme typical of DECO*27's early work. In maimai, むかしむかしのきょうのぼく was added as part of the GreeN PLUS update on September 4, 2014, making it one of the earlier Vocaloid inclusions in the series. Its Master chart, designed by the pseudonymous charter 某S氏 (a certain Mr. S), has undergone significant level re-evaluation across maimai versions, starting at level 10 in GreeN PLUS and eventually settling at level 12 in the FESTiVAL era and beyond, reflecting the community's evolving understanding of its challenge. The Expert chart was designed by mai-Star, a regular contributor to the maimai chart roster. The song is categorized under the niconico & VOCALOID genre and remains available on Japanese-region cabinets.