That song also introduced me to the woman whom Mom had brought up from time to time when there was mention of Chinese/Taiwanese-Japanese singers. And that lady happened to be Teresa Teng. I'd always heard that she was extremely popular in both the Japanese and Mandarin/Cantonese music industries before she passed away in 1995, but I never got what the big deal was about her - I didn't bother to listen to her songs at that time.
Anyway, it turns out she had her own rendition of 'Imademo...' too. As I was of a simpler mind back then, I assumed that she was doing a cover of Aska's song since I listened to his version first and also because he wrote and composed it. It was only about a year later when reading through the list of songs he had written (lyrics, music or both) for various artistes did I realise that it was the other way around. The song was supposed to be for Teng, and Aska was the one doing the self-cover!
I couldn't find much on the song, all I know is that it was released in 1985 according to Chage & Aska's website, 2 years before Aska began his solo career. There wasn't any write up on the song, let alone mention of the song in Teng's discography on the J-Wiki... or on any Wikipedia page or website on her, so I don't suppose it was a popular song. I think its underrated, if you ask me. As for Aska's version, it was released as a track in his first solo album in 1988, SCENE with a different arrangement.
Now that I have listened to both versions, I can't say that I have a clear favorite since both are good in their own way... ... Yeah, and now I understand why Teng was so popular. She had a nice, sweet voice that complimented her innocent-young-thing image. I actually first heard her sing while listening to her rendition of the Enka song 'Naniwabushi dayo jinsei wa' (浪花節だよ人生は) not too long ago, and that immediately changed my mind about Teng being a tad overrated.