I've just done a
characters/seiyuus page for this show and was surprised to learn that half the cast is under 17. Talk about a youth movement in anime. Not just Kido Ibuki (now 15, Akiko in
OniAi) as Kyouro's
imouto, but also Morohoshi Sumire (13, the star of
Aikatsu) as Mao's
imouto.
Kirara's seiyuu Arakawa Chika is also just 13. Her little sister is played by Aoi Wakana, 14. Both of them are child actresses on TV and in movies. Megu's seiyuu Miyamoto Yume is all of 16.
We also get to hear Uesaka Sumire (21, Dekomori in
Chuu2Byou) as Tama. Mimori Suzuko (26, Sherlock in
Milky Holmes) does a nice job with Shion. Of course, Uchida Maaya (23, Rikka in
Chuu2byou) plays Mao. She is very effective sometimes, but sometimes seems to me a bit out of control.
Actually, a voice that has struck me as much as any is that of Tsunematsu Ayumi, 29, who plays the maid Mori-san.