You and Shadowheart have been growing a close bond for a while. She doesn't find any romantic interest in you, although you clearly have a more than platonic interest in her. She teases you about this. But Shadowheart has been feeling some doubt lately, in your connection. She's taken the time to do some divination with Lady Shar, and she come to a conclusion.
She asks you to meet her after the others are down, telling you there's something you need to discuss. She doesn't think you're taking this connection as deeply as you feel it to be, you haven't done enough to prove yourself to her. And what way does Shadowheart think you need to prove yourself to her? An offering of loss of self, a loss of your human dignity; she needs you to go through humiliation and embarrassment. The most disgusting, dehumanizing thing she can think of? Using you as a toilet. Will you be able to go through with it? Can you prove yourself to Shadowheart and Shar?