I've had a dumb idea for awhile now about a princess falling in love with her dragon captor, but all she gets to interact with is the back half of the dragon, particularly the tail. She is kept in a cave that the dragon uses its bulk to block the entrance of, and it just checks to see if she's still there by feeling around with its tail.
The dragon would have multiple weapons imbedded in its front half, lacking any hands that could get a good grip on the blades. It's back half is of course unscarred because this dragon has never saw fit to retreat or otherwise turn its back on an opponent. If the princess could just reach that front half, maybe she could pull a sword out and fight back. The dragon of course tries to keep her away from the front half of its body, so she has to earn its trust a bit by massaging the tail.
These tail massages would start with the tip, and the princess would see how far along the tail the dragon will let the massage reach. The ventral plates along the underside of the tail serve as a measure of progress in how far the dragon's trust goes. Along the way, her interest in getting close enough to retrieve a weapon shifts into interest in getting closer to the dragon. She also has to fight off the sexual thoughts developing towards that dragon butt that she's been working her way towards.