A striking fact regarding modern Japanese surnames is their sheer number. There's no precise count, but the consensus is that there are more than 100,000.
That will not astonish an American, whose melting-pot country harbors representatives of most of the world's ethnicities and is consequently home to perhaps a million surnames; or a Finn, for Finland, with barely five million people, has tens of thousands of surnames — the most in the world in proportion to population.
But compare Japan to its neighbors China and Korea.