Yes, Japan does have the fifth largest defense budget in the world, but when you consider that the US defense budget it more than the defense budgets of the next 10 spenders combined, it's not really that much for such a large economy.
Also worth noting, the US maintains significant military presence in most of the world's top military-spending countries. For obvious reasons, China and Russia have very little military US military presence, but Saudi Arabia, the UK, France, Japan, Germany, and South Korea all have significant US military presence on their soil.