Kagami Seira was born Sara Arbour to a French-Canadian father (who is half French and half Polish) and a Japanese mother on June 13, 1987. She grew up in Tokyo, Japan with her two younger sisters and currently holds Dual Citizenship to Canada and Japan. Kagami has stated that though she is fluent in English, she first learned the language in an International School in Japan.
In the year 2000, Kagami signed with the Now Fashion Agency, and began her career as a Fashion Model. She began modeling in teen magazines such as CUTiE, Seventeen, and Zipper. Her sister has also modeled with her current agency, and Kagami is friends with fellow Japanese / French-Canadian, Marie, who is also a fashion model. In 2001 Kagami appeared in her first CM for a Wedding magazine called Zekushii, which was followed by adding a voice over to a CM for J-Phone. Kagami then began to appear in various CM's , but she decided to enroll in University of Toronto. In 2007, Kagami returned to Japan to continue her career. Since her return she has steadily appeared in various CM's, promoting for products such as Freeplus.
Kagami began her music career on a compilation album titled a piece of water released by a-head records in 2006. She contributed two songs titled "Loose" and "Don't Leave", and was featured along side artist's like Lisa Cristobal Miyake and Kawabata Megumi with the final track "Christmas is...".