Raised in a wealthy family, her grandfather is the major shareholder of Tomoe Industries, she began music training with jazz singer Sanae Mizushima [ja] at the age of sixteen.
She enrolled in Nihon University College of Arts to study television direction and originally wanted to produce music programming for Fuji TV.
[1] Sagara debuted as a singer with the song The World for Two People (Japanese: 世界は二人のために), which won her the Best New Artists Prize at the 9th Japan Record Awards in 1967 and sold 1.2 million copies.
[3] Beginning in 1967, Sagara was invited to sing at the Year-end Song Festival, known as "Kōhaku", hosted by the Japan Broadcasting Corporation (Japanese: Nippon Hōsō Kyōkai, NHK).
[10] In 1980, a woman claiming to be Sagara's former partner outed her as a lesbian on TV Asahi's Afternoon Show, causing the collapse of her career.
[11][2][12] Sagara denied the alleged affair and the woman retracted her statement, but the damage was done, as invitations to the premier award shows disappeared.
[12] She did continue to work in music for a few years, releasing a single YASUKOの場合 (Yasuko case) in 1983[7] and then a jazz album to honor her former teacher Mizushima in 1986.