Dating girls in the post game needs some work. I've tried 5 girls, 2 crash when starting the scene, the other 3 I have no idea what to do even after going everywhere and talking to everyone.
There's also no full save with those scenes unlocked and they are the best ones.
I got one crash so far on the dates, when I started the game again and did the same date again it worked just fine, so you might want to just try again.
So far I have found the answers to four of the dates.
Shepe/Nun: go to the pond in center of town where the kids are swimming
Vanie/Bunny girl/Bar maid: go to the beach for a scene then go to the bathhouse, after the first sex scene in the bathhouse talk to her again without leaving the bath.
Teimi/Green Lion: talk to the nun/Shepe, the loli/Suzu, and the bunny girl/Vanie.
Marian/Crepe girl: Go to Vanie's house and go to the bed, Vanie's house is the one just below the teleport cat south location.