Instead of the girl getting free taps on your love meter they have a much slower refilling action bar and if there is action from them they take extra love as well. Of course this only applies in coitus, you can't sync them up anywhere else. A few extra tips, if you're not quick on the keyboard I can under this being a bit difficult if you're not using slow. (I didn't and still 'won' "battles" so the game is very possible if you learn the system.) Keep an eye on the dialogue, try to catch how the girl is responding to certain attacks. Also sitting on dialogue disables the action time if you need to slow things down, so there's that too.