A decent effort. As said, there were lots of grammatical errors. I don't find those so annoying though.
The work-around is a bit of a hassle from time to time. The buttons change their places often when there are sentences going on. So, maybe a bit more aligning or something.
Voice acting, hmhh, decent effort I'd say. Honestly I didn't put too much notice on it.
Overall the scenes are flowing well. One bug is buying the extra scenes. The scene doesn't stay available when you have bought it, as in you must play again to get the 4000 yen. Some guys are here for the hentai you know ...
As for that matter, it's quite good I think! Not over-the-top, not too crazy. Clean, if it fits.
So thanks for making this and maybe you'll have the strenght to correct some of the stuff or make more interesting flash games!