There are two artists who have used this name: a modern singer and Steffanie Borges, the singer of 1985's Urusei Yatsura theme tunes.
1. ステファニー (aka romanised Stephanie), is a Japanese singer who debuted in 2007 with the single "君がいる限り" and is with Sony Music Japan. She has an Armenian-American father and a Japanese mother, and lived in California until she was 14. When she was in California she sent demo material to music producer Joe Rinoie, who was very impressed with her. Because of this she traveled to Japan in 2002. Currently she is enrolled at Aoyama Gakuin University and studies law. Initially, before she debuted, not even her face was revealed. Reputedly she can sing in five octaves.
Real Name: Unknown
Blood Type: AB
・「君がいる限り」 - 2007.05.30
・「because of you」 - 2007.08.29
・「Winter Gold」 - 2007.12.12
・「フレンズ」 - 2008.01.30
・「Changin'」 (ステファニー feat. 田中ロウマ) - 2008.07.23
・「Stephanie」 - 2008.03.05
Sites: http://Steph.Jp (official - requires Flash)
2. Steffanie Borges is a Japanese-American who also fronted the Japanese metal bands Pink Noise and Show-Ya. Her "Hideaway" album contains both "Born to Be Free" and "Rock the Planet" in English.