The factor most responsible for the increase in Japan's dependency ratio is the "Increase in life expectancy."
This is because, with the increase in life expectancy, Japan has a high number of older adults. These older adults often pay little or no taxes.
A high dependency ratio is a depending ratio that is greater than 62.5
In Japan, the dependency ratio is 69.1, and the reason can be traced to the increased life expectancy of its population.
Hence, in this case, it is concluded that the correct answer is Increase in life expectancy.
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