Double is the stage name for Japanese R&B singer Takako Hirasawa (平澤貴子, Hirasawa Takako) (born March 14, 1975). Double used to be the name for the two member R&B group consisting of Takako and her sister Sachiko (1973 - 1999). After the death of Sachiko, Takako started her solo career adopting Double as her stage name. Double has been titled as the "Queen of R&B" and is considered to be a pioneer for being the first artist to bring American-style R&B to Japan.
Source: “Double (singer)”, English Wikipedia (CC BY-SA 4.0), excerpt