This is clearly not Kimura Ryouhei,
(sadly), I have 23 cds of Kimura-san and have listened them a hundred times, I’m sorry to tell you it’s not him (though it slightly ressembles, I was too excited when I listened to this cd).
I believe this is from Futari no Himitsu Vol. 08 (I’m 70% sure, careful), and its seiyuu is Nakazawa Masatomo.
Kimura-san doesn’t, and never did R18 drama cds.
Although, I recommend that you listen to Nakazawa-san’s R18 cds, they’re very… interesting
（☝ ՞ਊ ՞）☝ His voice is different than in this one, much more sexy and deeper.
Check my drama cd list, you can find some of his :)
EDIT: I’ve been told that this track is from Trick and Alice’s tokuten cd, which is apparently an R18 otome game. You can download it for free on Bishie Craziness’ blogspot (no hot-linking!) Thank you to lost-time-memery and shin-hae for providing me with the info.
I apologize once again for my mistake! OTZ
If anyone finds any nsfw cds from Kimura-san, please do tell me ehe