I've recently been following runonpu on deviantart and he's just finished a game in which you are given a month to help a young girl gain massive amounts of muscle. I'm not sure about the specifics of the game since my computer can't display Japanese characters correctly, but he is working with others to produce an English version. Here's his DA account:
http://runonpu.deviantart.com/
You should be able to follow the second link in his journal comments to his blog. (?) Go to his latest post to get the link to the download site. Once there, press the button to the right of the orange button to download the game.
Here's the largest progression I've been able to get in the game: