Winning via sexual attacks requires a good stamina and energy, willpower to restore energy doesn't hurt. That the path I'm on right now, and I haven't lost a single battle this playthrough. Unfortunately, it is still taking me a while for each fight, and I don't have much control over what happens. I put everything I could into manufacturing a super high energy score. What I did not account for is that Dexterity has a strong effect on inflicting pleasure damage and agility determines the speed of your attacks, and presumably turn order. If you want to not just "survive until they wear themselves out" but actually take them down sex-ninja style, than you're going to want to balance in dexterity and agility. Sex attacks also do more damage as they increase in their own levels. Practice makes perfect.
I am still unclear on what effect charm has. I presume that it either makes them want to do sex attacks instead of regular attacks, makes them take pleasure damage faster, or both.