Updating the "who voices who" list now that the post-retcon cast list has settled into something reasonably stable...
Aya Hisakawa still holds the title of hardest-working seiyuu in Refuge, * voicing Ami Mizuno, Arisa Sono, Lindy Harlaown, Miki Kaoru, Sarah Dupont, Skuld, and (usually) Kerberos. (And, eventually, an original character closely based on Ami so it makes sense that they'd share a voice)
Takehito Koyasu is a close second, voicing Fool, Jean Croce, Tou Ryuga, Touga Kiryuu, Yuichi Kayama, and (sometimes) Yosho.
Third place is a three-way tie with five characters each, between Ayako Kawasumi (Aoi Sakuraba, Artoria Pendragon, Ayumi Tokita, Kay, and Mahoro Ando), Kikuko Inoue (Belldandy, Chitose Hibiya, Electra, Kasumi Tendo, and Steel Angel Nadeshiko), and Rie Tanaka (Chii, Chizuru Aizawa, Koyomi Mizuhara, Maho Nishizumi, and Steel Angel Saki).
Three seiyuu voice four Refuge characters each: Kana Ueda (Hayate Yagami, Honami Takase Ambler, Mii Konori, and Rin Tohsaka), Michie Tomizawa (Manami Kasuga, Rei Hino, Sumire Kanzaki, and Linna Yamazaki), and Megumi Hayashibara (Atsuko Natsume, Nam, Rei Ayanami, and (sometimes) Ranma Saotome).
There are more seiyuu who play three characters than I care to count at the moment; I'll just mention (to show off their range) that Asami Sanada plays Chizuko Oe, Sawako Yamanaka, and Vita, and Megumi Ogata plays Haruka Ten'oh, Shinji Ikari, and Yukito Tsukishiro.
Possibly of more interest is the "talking to themselves" list. Not including canon cases of one seiyuu playing multiple roles in a single work:
* Unless you count the Misaka Sisters as separate characters, in which case Nozomi Sasaki has over nine thousand roles, all named Misaka.
Aya Hisakawa still holds the title of hardest-working seiyuu in Refuge, * voicing Ami Mizuno, Arisa Sono, Lindy Harlaown, Miki Kaoru, Sarah Dupont, Skuld, and (usually) Kerberos. (And, eventually, an original character closely based on Ami so it makes sense that they'd share a voice)
Takehito Koyasu is a close second, voicing Fool, Jean Croce, Tou Ryuga, Touga Kiryuu, Yuichi Kayama, and (sometimes) Yosho.
Third place is a three-way tie with five characters each, between Ayako Kawasumi (Aoi Sakuraba, Artoria Pendragon, Ayumi Tokita, Kay, and Mahoro Ando), Kikuko Inoue (Belldandy, Chitose Hibiya, Electra, Kasumi Tendo, and Steel Angel Nadeshiko), and Rie Tanaka (Chii, Chizuru Aizawa, Koyomi Mizuhara, Maho Nishizumi, and Steel Angel Saki).
Three seiyuu voice four Refuge characters each: Kana Ueda (Hayate Yagami, Honami Takase Ambler, Mii Konori, and Rin Tohsaka), Michie Tomizawa (Manami Kasuga, Rei Hino, Sumire Kanzaki, and Linna Yamazaki), and Megumi Hayashibara (Atsuko Natsume, Nam, Rei Ayanami, and (sometimes) Ranma Saotome).
There are more seiyuu who play three characters than I care to count at the moment; I'll just mention (to show off their range) that Asami Sanada plays Chizuko Oe, Sawako Yamanaka, and Vita, and Megumi Ogata plays Haruka Ten'oh, Shinji Ikari, and Yukito Tsukishiro.
Possibly of more interest is the "talking to themselves" list. Not including canon cases of one seiyuu playing multiple roles in a single work:
- Ayako Kawasumi: Aoi Sakuraba and Ayumi Tokita are both at Aria House.
- Rie Tanaka: Chizuru Aizawa and Koyomi Mizuhara are also both at Aria House.
- Chinami Nishimura: Aria Pokoteng is at Aria House and Mia Guillem is practically next door at Kaleido Stage.
- Kaori Mizuhashi: Taeko Minazuki is at Aria House and Rosetta Passel is practically next door at Kaleido Stage.
- Ryou Hirohashi: Alice Carroll is at Aria House and Sora Naegino is practically next door at Kaleido Stage.
- Sayaka Ohara: Alicia Florence is at Aria House and Layla Hamilton is practically next door at Kaleido Stage.
- Junichi Suwabe: Ren Nekoyashiki and Archer are both at Appartements Mont-Royal Sud.
- Kana Ueda: Honami Takase Ambler and Rin Tohsaka are also both at Appartements Mont-Royal Sud.
- Lisa Reimold: Tess Pastorius and Zion are both found somewhere in Basin and Range Province. Tess is specifically identified as being mobile.
- Masami Kikuchi: Kazuki Sendo and Keiichi Morisato are both at Douglass Gardens Apartments.
- Ai Orikasa: Fujieda Ayame and Reiko Amagi are both at the Grand Imperial Theatre.
* Unless you count the Misaka Sisters as separate characters, in which case Nozomi Sasaki has over nine thousand roles, all named Misaka.