We were discussing the impact of the Supremes in Japan, but I think that it's Diana Ross that had an impact in japan.
In the seventies, this was called "Black Sound" by the press and promoters like Kyodo Agency.
Dionne Warwich and Donna Summer, all had success here, but nothing as enduring as Diana. In a US TV show, she stated her best audiences were UK first, than Japan.

Diana on the Oricon charts. Her albums used to sell from 50.000 to 200.000 copies.

Albums 1972/03/5 Lady sings the blues [[soundtrack) # 91
1973/09/25 Touch Me In The Morning # 67
1974/02/15 Diana & Marvin # 19
1974/03/10 Last Time I Saw Him # 49
1974/05/05 Best Collection # 67
1976/05/01 Diana Ross # 27
1978/05/25 Diana Ross # 74
1979/07/25 The Boss # 66
1980/06/21 Diana # 33
1981/05/21 To Love Again # 68
1981/11/21 Why Do Fools Fall In Love? # 28
1982/11/01 Silk Electric # 33
1983/07/25 Ross # 35
1984/09/29 Swept Away # 32
1985/09/28 Eaten Alive # 24
1987/06/21 Red Hot Rhythm & Blues # 60
1989/06/14 Workin' Overtime # 98
1991/07/26 The Force Behind The Power # 21
1992/03/29 That's Why I Call You My Friend # 33
1993/05/26 Stolen Moments # 83
1993/11/24 One Woman Ultimate Collection # 46
1994/12/07 A Very Special Selection # 66
1995/09/27 Take Me Higher # 36
1996/12/18 Voice Of Love # 91
1997/02/05 A Gift Of Love-TV Tie-In Compilation[Japan Only] # 31
1999/06/09 Every Day Is A New Day # 95
2001/10/27 The Very Best Of Diana Ross-Love & Life # 22


Singles
1974/02/05 You Are Everything # 82
1980/07/21 Upside Down # 48
1981/09/05 Endless Love # 33
1990/01/25 If We Hold on Together # 4
1992/03/29 That's Why I Call You My Friend # 58
1997/02/08 Promise Me You'll Try # 86