Actually, there isn't. Inflation/deflation isn't just a function of the amount of money, but of the speed of circulation, as well. If people are just sitting on money,... well, they can "just sit on" arbitrarily large amounts of it. If the BoJ gave a hundred zillion yen to the major banks, which then just sat on it and neither lent nor invested it (which is not a bad move in deflationary times), then the effect on inflation of that money creation would be zero.
The problem with what the BoJ and Japanese government have been doing isn't just in the amount, but in the obvious half-heartedness and temporariness of the measures they've been taking, which are exactly the sort of features that make people not want to invest windfalls they get from money creation. For that matter, it's the same (lack of) stimulative effect we saw with the last round of Bush tax cuts, which didn't actually stimulate anything, because people correctly recognized them as a one-off windfall and most people used them to pay off existing debt, or to put into savings (that weren't being lent out, this being during the credit crunch) instead of to spend on consumer goods and stimulate the economy.
And we'll probably see the same thing with the next round of one-off cuts; in fact (although I can't find the article now), that's exactly what CNN is recommending people do with their expected windfalls....