"who are you?"
I am realizing now that another reason this line hit so hard was that, on top of Syril only realizing now that Cassian does not think about him, doesn't even know who he is, is that I myself as the viewer was also only realizing now that Cassian does not think about Syril, nor even know who he is.
This whole series as the viewer we are cutting back and forth between their tangled storylines, you watch Syril obsess over Cassian, but I didn't realize that you must never see a scene of Cassian thinking about Syril. It kind of thrills me, for my next rewatch, to clock that.