Tomoko Kawakami, Fuyuki's original voice actor, passed away on June 9th at age 41 after a 20 month battle with ovarian cancer.
Kawakami-San played Fuyuki for the first 230 episodes and first 3 movies of the anime before going on sick leave and being replaced by Hōko Kuwashima. She also had roles in Bleach, Pokemon, One Piece, Angelic Layer, and Super Smash Brothers: Brawl and many, many more series, video games, and Japanese dubs.
Since I've seen few episodes beyond the American release of Sgt. Frog, Tomoko Kawakami is still who I hear in my head when I think of Fuyuki speaking Japanese. She brought a wonderful voice to the role, and it's terribly sad to learn that she left us at such a young age.
Source (Bulbapedia)