Which set of powers allows the president to send representatives to china and japan to represent his policy

Military. Unlike most European countries, the United States constitution considers sending diplomatic delegates and representatives to foreign countries as actions of defense and war, not foreign relations or diplomacy. The Founding Fathers were heavily influenced by Carl von Clausewitz, a widely known figure in the years leading up to the Revolutionary War. He famously stated: "War is the continuation of politics by other means."

And this too use this if needed