Artist: Siam Shade
Song: 1/3の純情な感情 (1/3 no Junjou na Kanjou) (1/3 True Feelings)
Album: Siam Shade IV - Zero
Year: 1997
Notes:
Made this in a flash and experimented with the subtitles a bit. I thought I had a non-Charm version but I guess I didn't? You can see the Spanish subs at the top still, sorry!
http://www.animelyrics.com/anime/kenshin/rk1third.htm
https://en.wikipedia.org/wiki/1/3_no_Junj%C5%8D_na_Kanj%C5%8D