A suggestion:
Purity Disabling Perk, gained from defeating the Demon King.
Disables Purity Loss, either in Combat or Encounters, allowing you to enjoy your post-quest indulgences! Allows you to Pass/Fail Slut checks at will.
I wanna suck dick, now that I've beaten both a Huge Snake and a Huge Dragon. I've earned some R&R that doesn't make me feel bad for losing Purity, my quest is over!
Hells, I kinda want some post-Demon King battle Encounter Variant Conditions. Being a bit proud of your victory and boasting about it or realising that you've done enough to consider retiring as a Hero with people you normally wouldn't. Glory has been earned, now is the time to earn some peace and quiet.