Vocalist Ringo Sheena originally debuted as a solo musician in 1998, however decided to become a member of a band instead for her main musical activities, and debuted Tokyo Jihen in 2004. After their debut album
Kyōiku, two of the original members of the band made decisions to leave, and were replaced by pianist Ichiyo Izawa and guitarist Ukigumo. The new line-up released the single "
Shuraba", a song used as the theme song for the drama
Ōoku: Hana no Ran., and the band's second album,
Adult (2006).
Adult, while featuring lyrics entirely written by Sheena and the band collaborating to arrange the songs, also featured "Himitsu", which was arranged solely by Izawa, and "Tegami", which was composed by Izawa and arranged by Sheena. In late 2006 and 2007, Sheena briefly resumed solo activities in collaboration with
Neko Saito, on
Heisei Fūzoku (2007), a soundtrack album for the
Mika Ninagawa film
Sakuran. The "OSCA" single was first announced on May 17, 2007. The
Variety project for the band involved the band members other than Sheena amassing demo tapes, and the band making careful selections. For the project, Sheena worked as a vocalist and a lyricist. During the single's release schedule, the
Toshiba stake of Tokyo Jihen's label
Toshiba EMI was bought out by the
EMI group. The label was renamed
EMI Music Japan on June 30, 2007. == Writing and production ==