Well the knife(or at least how it was presented at the end of the last chap) was a red herring. Not really surprised, and am actually glad to see Rei trying to comfort her. Unfortunately she no longer wants to die with Reiji.
From the way he was holding his head, there was definitely some frustrations; he did essentially chose Yuko over her at a critical moment in her life, which was one of the main components that led her to were she is today. Now the person whom he once heralded as the brightest element in his life wants to die with the man he swore never to see again. To be Reiji, is to suffer =0(... I guess this at least puts him in the position to see Nagi again. Makes me wonder if, this time, he will invite her to die with him, instead of the other way around, like in the beginning.