Kinky Hermione/Ron in background?
This is a Snarry fic I read years ago, and I remember very little of it except that there were snippets of Hermione and Ron's relationship - I think Harry was asking for Hermione's help with his relationship with Severus, maybe about how to spice things up in the bedroom, and it gave Hermione ideas? She was getting a little kinky, taking on the dominant role with Ron - I'm pretty sure I remember her wielding a crop at one point. I think it probably 'faded to black' before she actually used it - it was definitely a Snarry, so the Hermione/Ron stuff was mostly implied or left to the reader's imagination, which as the things left to the imagination often do made it stick with me more than anything else.