Sumi Shimamoto, real name Sumi Koshikawa, is a veteran Japanese voice actress born on December 8, 1954, in Kōchi, Kōchi Prefecture, Japan. After graduating from the Toho Gakuen College of Drama and Music, she joined Gekidan Seinenza, a theatrical acting troupe. She is currently independent of any talent management company.
She is married to Daisuke Koshikawa, one of the founders of the comedy troupe Chibikko Gang.
Her best-known voice roles include Nausicaä in Nausicaä of the Valley of the Wind and Kyoko Otonashi in Maison Ikkoku.
She won the role of Nausicaä as she had played Clarisse in Lupin III: The Castle of Cagliostro and impressed Hayao Miyazaki. Patrick Drazen praised Shimamoto's acting in a scene where Nausicaä stops an insect from diving into an acidic pool by getting in its way. Nausicaä is burned by the acid and she screams. Drazen described this scream as being one which "tears at the listener and raises the bar for cartoon voices".