The WSJ has it here:

Tokyo’s move is striking because its political class has long behaved as if tax rates don’t matter, and the government is wrestling with the need to finance a typically large budget deficit and an aging population. But in 2010 politicians had a radical idea: Cutting the corporate profits tax would boost economic activity and lead to higher revenues.
The government approved an overall five percentage-point cut, which was delayed by last year’s earthquake and tsunami. But the first installment arrives April 1 and in three years the rate will drop another 2.3 percentage points to 34.5%.