Does anyone know what this story is called by a vague memory of a particular scene?

I think it was supposed to be a NMMxTwilight shipping, and it had NMM take Twilight as some sort of slave or something and basically treat her really cruelly and brutalise her. Then assassins tried to kill NMM, but despite this fixing everything for Twilight, the unicorn decided to stop them in their attempt, and then NMM killed them.