I've never really been particularly interested in a seiyuu cast of a series, although the past few months I've been able to familiarize myself with some notable names. Or at least, some seiyuu that, one time or another, I have heard before.
(Disclosure: I was a serial
hentai watcher before I started watching animé.)
Mamiko Noto, the voice behind the innocent
Sawako from
Kimi ni Todoke, happens to be the super badass Rin in
Mnemosyne (probably my favorite mature OAV to date).
But the most [pleasant] surprise I've had is that
Akira Ishida, whose only role I actually know is
Gaara from
Naruto, also voices the male protagonist in
Moonlight Lady. The OAV is friggin' hardcore, if I may say so myself. It's not as if it's a cheap-quality hentai, but really...seriously?
And now I can't get rid of Gaara having sex with the character Suzuna (!!!), a character first voiced by
Sanae Kobayashi, who, incidentally, voices
Namie Yagari (Durarara!!) (among others). I can't help comparing their voices in those "normal" series to the ones they use in the OAV (moans and groans and screams of pleasure and all). I think I'm scarred for life.