Los Indios has been around since 1962 playing their izakaya & bar-friendly Mood Kayo and Latin-tinged music. In 1968, they had a huge hit with "Como Esta Akasaka"(already profiled), and then 11 years later, the group had an even bigger hit with "Wakarete mo Suki na Hito" (Even If We Part, I'll Still Love You). And for the first time, Los Indios invited a female vocalist to sing with them, Silvia.
Silvia, who was born as Rieko Matsuda（松田理恵子) in 1958, was scouted while singing at an establishment owned by another singer/TV personality, Mitsuo Sagawa（佐川満男). Her first known assignment was with Los Indios, and the pairing was a fortuitous one since "Wakarete mo Suki na Hito" ended up becoming the 8th-ranked song for 1980 after its release in September 1979. Listening to it (along with similar songs of the genre) reminds me of some of those high times Tokyo must have been having back then, and this was even years before the Bubble Economy.
The pairing of Los Indios with Silvia started a tradition that has lasted up to the present day. Besides Silvia, 7 other female singers have worked with the group, and the 9th singer, Nina, a jazz singer, will be joining as of December 15 2012 according to J-Wiki.
As with a number of songs in kayo kyoku (such as Hiromi Iwasaki's "Sumire Iro no Namida"), the successful version has often concealed its previous versions. That has been the case with "Wakarete mo". Originally, singer-songwriter Ben Sasaki（佐々木勉) had created the song for the Group Sounds band, Purple Shadows, as their 5th single in November 1969. That version is above. It wasn't a hit for them, and some years later in 1975, the leader of Los Indios, Shizuo Tanahashi（棚橋静雄), did his own solo version of the song without it becoming a hit.
Its popularity as a duet song hasn't been lost even on the professional singers. I'm sure a lot of them on the various TV shows have gotten together to do their take on the Mood Kayo classic. Here are Hiromi Go（郷ひろみ） and Junko Sakurada（桜田淳子）.
And heck, how about a real surprise? Not sure which show or when this came up, but even the boys from B'z and comedienne Kuniko Yamada（山田邦子) did their take. Enjoy!