Until day 10 there are five unlockable naughty scenes with their corresponding CGs, so I gather you've seen one of them. Each one happens with a different character and to unlock them you must make good decisions and score enough points with the character in question. Good luck :3
I already wrote it in another comment as well, but I'll tell you. There is one on day 5 (not Erik's), on day 6, 8, 9 and finally on day 10.