I think I've determined a few things:
1. Purity and Energy don't do anything.
2. Arousal can increase but the triggers for its decrease don't always work, and you remain Overwhelmed at all times if your Arousal has ever reached maximum regardless of its current value.
3. There are for some reason always three people in sex scenes, rather than what is probably the intended up to three, and if there's only one physical person it will slot in nonexistent people with the same name who can't properly be interacted with.
4. NPCs sometimes just use the wrong words for body parts/actions in sex scenes.