Oh! You're quite welcome. I was hoping I'd find some clues on the original, but no luck.
I don't know how to parse more than very rudimentary Japanese, but with the help of that knowledge and a few translators and dictionaries (to check myself) I left a comment on the picture to ask Hoppege who she is. Maybe we'll get a reply.
malus said: Well I can't be sure, but after checking around here I think that sakurasawa_yuna and isaku are the closest I can find.
It would be someone voiced by kugimiya_rie, though, which I believe disqualifies sakurasawa_yuna. I couldn't find much on the other character you mentioned.
As best I can tell from my brief researching, Isaku and its sequel Shusaku were Japanese survival horror hentai games (What a combination, amirite? Leave it to Japan.) There were some (also adult-oriented) OAVs released about them.
The girl in that picture isn't named Isaku (at least, as best I can tell) but I'm not exactly sure what her actual name is yet. Not that it particularly matters for this because judging from artwork and shots from the game, the school uniforms in the series don't look like the one in this picture. So... the question remains.