Masayoshi Son, SoftBank Group Corp.¡¯s billionaire founder, checks the chart. Then again. Another time. And once more for good measure.

Lately it¡¯s only moved in one direction: up.

It¡¯s not a chart of the firm¡¯s stock picks. Those are sinking fast. So too is Son¡¯s fortune ¡ª at $13.7 billion (?1.6 trillion), it¡¯s crashed $25 billion in the past year, according to the Bloomberg Billionaires Index.