The voice-acting was not left to chance in this series. They hired some of the best.
Ueda Kana (Hazumu) got our attention with Yumi in Marimite and I think is the moe-est voice around. Just perfect for the moe (?!) Hazumu. The only thing to wonder about is how little difference there is between her voice as male Hazumu and her voice for the rest of the show. Little, but it is different.
Horie Yui (Yasuna) really got me with her work in episode 4. I am only learning to love Hocchan, but this performance helps a lot.
Tamura Yukari (Tomari) in person is not the image of the tomboy, nor is her voice at all low. But she, like Hocchan, almost made me cry with her great work in episode 4.
Asano Masumi (Ayuki) is the dependable genki second-fiddle in a lot of shows (Uta~Kata, Mahoraba), and her quiet wisdom here is just as effective. She's a pro.
Ono Daisuke (Asuta) played Yukito in Air. That was his first big role, but there are more to come.
Even smaller parts have known actors in them: Fujiwara Keiji (Shuuji in Honey & Clover) as the spaceman and Shintani Ryouko as Jan-puu.
Hocchan and Yukarin (nicknames for Horie Yui and Tamura Yukari) are good friends and also form a singing duo called "Yamato Nadeshiko." They tend to dress gothic lolita when they perform....
There is a little raw video of a Yamato Nadeshiko photo-shoot on tokyo toshokan right now. I think it's okay to mention because it appears to be just something like an Entertainment Tonight TV feature. Poor quality, but quite entertaining. Made me realize why the group's shows are sold out. They have had two hits that were in the top dozen best-selling songs of their year.
I've linked some of the names above to entries in
Hashihime's Seiyuu Pages, where I've put photos, and links to more info.