I love Kasyrra with the fury of ten-thousand exploding suns and want the option to swear myself to her slutty service right from the very beginning. Seriously, a corruption run where you go full demon right from the get-go would be completely awesome. Slowly corrupting your own party members and bringing them to her side one by one would be grand. Frankly, any more content with her will be greeted with total glee from me.
Team up attacks, especially sexy ones. Use that shiny new party system to your advantage, and maybe even dust off your old Chrono Trigger memories. Using your martial, magical, and sexual skills in battle should take your team members into account, especially if you're already sleeping with them. The Dancer, for instance, should have the option of using a party member as a dance partner for the round, losing a turn for that character, but guaranteeing the aroused debuff procs.
Magic that can be used in sex scenes as well as battle. It always struck me as odd that despite knowing a spell to instantly arouse a target in the first CoC I could never use it on any of my lovers or even slaves. Knowing how to bend the fabric of reality to your will should really affect things more than just DPS potential. High-level knowledge of sexual magic should add extra bits to some scenes, or even add sex options that are otherwise locked.