This is the final part of my four-part Q&A series arising from my recent trip to Japan. In this post, I answer just one question. The answer goes to the heart of the relationship between the national government (finance division) and the central bank and illustrates the complexity of reserve accounting. So it needs some background by way of education. Recall that these questions about Modern Monetary Theory (MMT) were raised with me during my recent trip to Japan. The public discussion about MMT in Japan is relatively advanced (compared to elsewhere). Political activists across the political spectrum are discussing and promoting MMT as a major way of expressing their opposition to fiscal austerity in Japan. The basics of MMT are now as well understood in Japan as anywhere and so the debate has moved onto more detailed queries, particularly with regard to policy applications. So as part of my current visit to Japan, I was asked to provide some guidance on a range of issues. In my presentations I addressed these matters. But I thought it would be productive to provide some written analysis so that everyone can advance their MMT understanding.