This event has several "triggers", and on different versions of the game, they were slightly different.
To summarize, on the first day (evening) you need to:
- undress the princess as much as possible, the crown and dress should remain on, accessories such as bows or "necklaces" do not count.
- shift the color of the heart to the maximum blue spectrum, as much as the number of dialogues allows, while you can not "scold" the princess until the 3rd heart. It is the undressing that changes the color of the heart. And also the request to take off the crown gives the same effect as when undressing, but the princess does not take off the crown, this is a good way to achieve the desired mood without a "penalty".
- bring the princess to at least one orgasm and unlock the second heart. (on some versions it was possible to call the desired scene on the second day and with one heart, but this was extremely difficult to achieve)
And in earlier versions you just had to get as many hearts as possible. 3-4 hearts caused this scene, but 2 did not.