Mitsuko Horie is a well known and beloved singer with a long career in performing anime and tokusatsu songs. Not only did she perform the original theme song to Ninja Captor, but she co-sang the theme to Himitsu Sentai Goranger. She is also well known for such beloved theme songs as the original Sazae-san theme, Candy Candy, Majokko Tickle, and the 1988 version of Himitsu no Akko-chan. She actually did quite a few more themes than the magical girl ones, but those are honestly the ones that I know the best.
She also has quite a few voice roles: not only did she sing the theme to Akko-chan in the remake, she provided her voice. Her best known role in the west, no doubt, was Sailor Galaxia, the ultimate tragic villain in the long-running Sailor Moon series.
Being a huge Sailor Moon nerd, I would be remiss in my duties if I did not post this song. She has an amazing range and a powerful voice, and without spoiling too much about Akibaranger, I can honestly say that she's still got it.