
Quick answer — Kazuko Sugiyama voices Heidi in Heidi, Girl of the Alps, Serebii in Pokémon 4Ever, Amaranta in ARIA The ORIGINATION and 10 more characters.
Kazuko Sugiyama voices Heidi (Heidi, Girl of the Alps), Serebii (Pokémon 4Ever), Amaranta (ARIA The ORIGINATION), Hatsuna (Natsume Yuujinchou Go Tokubetsu-hen), Matsuura-san (The Summer Hikaru Died), Fuzuki Koyama (Looking for the Full Moon), Vreme (Galaxy Express 999), Kyouko Izumiya (Re: Cutie Honey) and 5 more.
Heidi is voiced in Japanese by Kazuko Sugiyama.