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Tear Jerker: Sunstone
The scene in Chapter 2 where a drunk and crying Ally tells Lisa what happened to Alan's ex-girlfriend Marion. See the Nightmare Fuel page for the rest.
The really heartbreaking part of that scene was Ally flashing back to Marion using the safeword in desperation to try to get her to untie her bonds, which Ally couldn't do for reasons outlined in the Nightmare Fuel page. For a domme like Ally, being put in a position where one has to break the rule of the safeword to keep someone safe is one of the worst experiences that one can go through.