Certain enemies can give you corruption after playing through the game:
- Slime Dragons will give you a corruption point each time Grove gets slime-suited.
- The water tentacles in the jungle add a corruption point each time Grove is grappled while naked. (Otherwise, they remove a piece of armour instead.)
Both of these actions lower STM, so be careful you don't get a game-over and lose your progress. Buy a few STM-restoring items if you have the funds.
You can gain more corruption on each trip using the Skimpy Covers (bandit "armour"), as they increase Grove's max-STM a bit.