I don't know what they meant by number of rounds, but I think pleasure stance eventually unlocks when your slut level get high enough.
If you are in the middle of your first run, I don't recommend getting going the slut route until either New Game+ or Free Mode. If you rack up too many passives without a viable slut build, you're going to lose every other fight, be forced to wait through the rape scene, start the next day with high fatigue and no halberd, and then come into this thread asking if there's anyways to remove passives,
like this guy. Basically, the slut build requires significantly more preparation and planning than grinding simply combat stats. It's much faster/easier to beat the game first than to fuck around too early and try to salvage the run.