Son used the placement, which raised 2.6 trillion yen ($23 billion), to pay down debt, buy back shares -- and fund high-tech bets by his Saudi Arabia-backed $100 billion Vision Fund.
The recent collapse in tech valuations is largely why the Japanese group is expected on Wednesday to post a 408 billion yen loss for the second quarter, according to consensus estimates.
"It cannot be helped that SoftBank's [WeWork] investment is seen as a failure," said Mitsunobu Tsuruo, analyst at Citigroup Global Markets Japan.
It also owns U.K. chip designer Arm, which SoftBank has on its books at $25 billion, and another $8 billion of assorted assets it classifies as "others."
Add all these assets together and the total comes to $256 billion -- or $130 billion more than the company is worth on the market.