Gee Wren, that's very helpful.. not.
Okay here's my take on it. The game in my opinion does not offer you any extra choices no matter what branches you take. Each girl is on a set track, and there are only two major points in each girl's storyline that makes any difference whatsoever.
The first choice that you get determines whether you will get to use the girl for the rest of the game. If you make the wrong decision here, the game will automatically lock out this girl and you cannot "play" with her for the remainder of the game. The green-haired girl for instance requires you to choose the first option when that blonde-haired guy shows up. If you make the second choice it goes back to the options screen and her name is permanently marked out. Every girl has a similar sequence like this except for the red-haired girl, who is pretty much your bitch for life in the game - she is always available to play with, as her first "big butt" transformation is pretty much forced upon you.
After you've figured out which options give you access to the girls, when you keep playing with them you will eventually come to a second "y-split." This second choice determines 1 of 2 different transformation paths for each girl. The red-haired girl for instance - option 1 is the "**12** branch" and option 2 is the "BE and ropes branch".
In order to max any girl out on percentage is simply a matter of making the right choice whenever the score appears on the screen along with a decision. You can save at this point, then make a decision and see if it was the right one - if not you can reload your game and pick the other choice, which will improve your score.
Playing this way, I have found that the game will give you enough time to "max out" two of the girls' transformations. If you try for three the game usually stops you all of a sudden and forces you to pick one of the two girls you've already maxed out. If dally around on more than three girls, or if you fail to max out 2 of the girls (or you fail to choose a girl you've already maxed out) by the time your time runs out, then the game ends without giving you any special scenes.
How to get the purple-haired lady could be finding the trick to max out 3 girls at once. However, nothing I have done yet has unlocked her. However, I still have more of the regular game to unlock (I didn't really feel like maxing out the **09**). I think perhaps the trick might be that you _have_ to max out the red-haired girl and then pick 2 of the others and just concentrate on them.
Another theory of mine is that certain options and orders that you choose to do things will open up more options down the road. Or as was said earlier you have to click a different mouse button or something. I don't really know. No offense but the game sort of got boring really quick for me. Even though all the CG is _fabulous_, it's still just lots of tedious mouse-clicking....