In the land that gave us Hello Kitty, it's no surprise the government employs an endearing mascot to sell its bonds. His name is Kokusai-sensei. A pint-size rendition of him welcomes visitors to the investor relations office at the Finance Ministry. Pudgy and professorial, he's got his own Twitter account and stars in an online manga.

Yet this publicity campaign seems rather unnecessary. There's just not much for Kokusai-sensei to do these days, thanks to the existence of a single, massive buyer of Japanese government bonds: the Bank of Japan. Why bother encouraging private investors to buy JGBs when the BOJ has been devouring enough of them to finance the bulk of the government budget deficit since Prime Minister Shinzo Abe took office in December 2012?

The central bank has clamped a tight grip on the bond market in an effort to pull down borrowing costs and inject massive liquidity — all to propel Japan out of the deflation and stagnation that took hold in the 1990s.