Graduated from Kunitachi College of Music, Department of Music Composition, Ōshima began her activities as a composer and arranger while in college, and has been involved in composing music for movies, commercials, TV programs, anime, ambient music and tunes for classical musicians. She released the first Symphony entitled “Orasho” when she was still in college. Through her masterful manipulation of both orchestras and synthesizers, she has attracted attention from various sectors for creating grandiose, dramatic sounds and beautiful melodies.
Ōshima was the youngest person to be awarded the 1st prize at International Electone Festival / International Electone Concours in 1977 when she was 16 years old. Her other awards include the 52nd(1998) and 67th(2013) Mainichi Film Contest Award for Best Music, the 21st(1998), 24th(2001), 26th(2003), 27th(2004), 29th(2006), 30th(2007) and 38th(2016) Japan Academy Prize (film award) for Music, and the 31st Japan Academy Prize for Best Score, Tokyo Anime Award for Best Music in 2006, Best Composer Award at Jackson Hole Film Festival 2007(in U.S.). Moreover, Ōshima has composed a large number of music for music festivals in France and Luxembourg, stages in Belgium or concerts in Japan and U.S.A. She also recorded and conducted with orchestras and musicians from all over the world such as U.S., Australia, France, Russia, Belgium, England, Czech, Austria, Poland, Italy, Hungary and Bulgaria, including a concert "KAIJU CRESCENDO: AN EVENING OF JAPANESE MONSTER MUSIC" at the G-FEST XXVI (2020) in Chicago. Ōshima was one of the 27 composers for the album ‘In 27 Pieces: the Hilary Hahn Encores’ performed by violinist Hilary Hahn which was awarded a 2015 Grammy Award in the Best Chamber Music category (she composed “Memories”). She has been engaged in many governmental projects as well, such as music director at “40th Year of ASEAN-Japan” in 2013, in which she supervised and managed musicians in ASEAN (Association of Southeast Asian Nations) countries, organized concerts in ASEAN countries and composed music for the ASEAN Summit.
2007: Le Premier amour (from the album "Smile" by Japanese violist Emiri Miyamoto)
2007: Amanda (with Kaori Muraji (classical guitar) and the Orchestre des Virtuoses de Paris)
2009: Concerto for saxophone (with Daniel Gremelle (saxophone) and the Tokyo City Philharmonic Orchestra)
2010: Concerto for viola (with Pierre Lenert (viola) and the Kyushu Symphony Orchestra)
2011: Ganbalo Nippon (short film The Orchestra in Hot Air Balloon for Japan[31])
2011: Vocalise (with the mezzo-soprano Irina De Baghy for Festival Sérénade in Surgères[32])
2011: Requiem ~ It lies at the bottom of the sea (with Ensemble Lucilin in Luxembourg)
2013: In 27 Pieces: The Hilary Hahn Encores (musical project with the violinist Hilary Hahn)
2013: Viola Sonata (with Pierre Lenert (viola) and Ariane Jacob (piano) for Festival Sérénade in Surgères in France)
2013: Concerto for piano quartet with Orchestra (with Musicians of Opera de Paris and the Kyushu Symphony Orchestra)
2013: The ASEAN-JAPAN "Drums & Voices" Concert Tour[33] (the 40th year of ASEAN-Japan friendship and cooperation project)
2015: Symphony No.2: Since 1945 (with the Kyushu Symphony Orchestra and Hiroko Kokubu (piano))
2017: Symphonic Suite "Sama" (with the Kansai Philharmonic Orchestra)
2017: Suite for Male Voice Choir "Message of the Voice" (with the Glee club of Tokyo Keizai University)
2018: "Augustus": Suite for Orchestra and Chorus (with the Kansai Philharmonic Orchestra and the Osaka Prefectural Yuhigaoka High School Music Department)
2018: Jin & Rin: 2 Rhapsodies for Clarinet, Marimba and Orchestra (with Richard Stoltzman (clarinet), Mika Stoltzman (marimba) and the Kansai Philharmonic Orchestra)
2018: Concerto for Koto and Shakuhachi (with Chiaki Endo (koto), Dozan Fujiwara (shakuhachi) and the Kansai Philharmonic Orchestra)
2018: Musical Sanza and Okuni
2019: Godzilla in Chicago - C.H.C.A.G
2019: Beyond the Point of No Return (with Japan Philharmonic Orchestra)
^"Nabari no Ou Staff Cast" (in Japanese). TV Tokyo. Retrieved 2009-08-06. 音楽: 大島ミチル(「鋼の錬金術師」、映画「椿三十郎」)" – "Music: Oshima Michiru (Fullmetal Alchemist, the film Sanjuro)