Seiko Niizuma is a Japanese actress and singer who was born on October 8, 1980, in Inazawa, Aichi Prefecture. While she is primarily known as a leading performer in musical theatre, she has also taken on select roles in anime voice acting. Her path to the performing arts began after she graduated from the International School in Bangkok and returned to Japan, where she studied International Relations Law at Sophia University. During her university years in 2002, she made her entertainment industry debut as a reporter for the TBS program King's Brunch.

Niizuma's professional career took a decisive turn in 2003 when she was cast as Éponine in the Japanese production of the musical Les Misérables. This role launched her career as a major stage actress, leading to further prominent roles in musicals such as Miss Saigon and Marie Antoinette. Her stage work has earned her significant recognition, including the 31st Kazuo Kikuta Theatre Award in 2005 and the 61st National Arts Festival Theatre Department Newcomer Award in 2006. She also received the 7th Tokiko Iwatani Award in 2016. Her vocal ability has been widely acknowledged, and she has released several albums, including Musical Moments in 2008 and Colors of Life in 2019.

Her voice acting work, while less extensive than her stage career, reflects the same vocal talent for which she is known. In the 2016 anime film Eiga Precure All Stars: Minna de Utau Kiseki no Mahō!, she was cast as the villain Sorciere. This casting was notably influenced by her musical theatre background, as the film was produced as the first authentic musical in the Pretty Cure series, requiring characters to perform songs as part of the narrative. She performed several songs for the film, including Hiyaku no Recipe and Majo no Komori-uta.

In 2017, she took on the role of Kiko-san in the critically acclaimed film Night is Short, Walk On Girl, directed by Masaaki Yuasa. In this film, she was part of a distinguished cast that included Gen Hoshino and Kana Hanazawa. Earlier, in 2011, she provided the voice for the character Chise Karino in the anime film The Princess and the Pilot, for which she also sang the theme song Toki no Tsubasa. These anime roles are distinct entries in a career overwhelmingly centered on live performance, demonstrating how her singing and acting abilities have been applied to animated projects when the opportunity arises.