Ahead of the visit to Tokyo by U.S. Defense Secretary James Mattis on Friday, the government appears to be missing a critical piece of information: How much does Japan pay to host U.S. military bases?

Tokyo has agonized over U.S. President Donald Trump's attack on so-called host-nation support, Japan's share of the cost of hosting U.S. military bases. Trump said on the campaign trail that Japan should pay more for the security umbrella provided by the U.S. military.

While news reports say Mattis is unlikely to demand more financial support during his trip to Japan and South Korea, there seems to be no consensus between Tokyo and Washington as to what percentage of the financial burden has been borne by Japan since 2004.