SoftBank Group Corp. is unloading part of its stake in wireless company T-Mobile US Inc. into a $21 billion contract, under pressure to secure capital following record declines in the group's investment business.

The deal is part of SoftBank's broader $42 billion pursuit to sell assets to finance stock buybacks and pay down debt, along with a plan to unload a 5 percent stake in its Japanese wireless subsidiary. Shares of T-Mobile fell around 1.5 percent in after-hours session on Monday.

Masayoshi Son, the company's founder, is dealing with huge losses in his Vision Fund after writing down the value from WeWork to Uber Technologies Inc investments in the sharing economy.

In a statement, cited by Sherisse Pham of CNN Business, given the current status where there's worry for a second and third wave of the coronavirus, "SoftBank Group believes that it needs to further enhance its cash reserves." Softbank issued the unexpected disclosure of its planned sale of $41 billion worth of assets in April to acquire shares back and cut debt.

SoftBank's shares have grown over 200 percent since middle of March, despite the economic doubts sparked by the COVID-19 pandemic, as Son moves to reduce the company's ownership in other firms like Alibaba Group Holding.

A large chunk of the T-Mobile stocks that SoftBank plans to unload were bought by T-Mobile itself, which will in turn unload them to the open market and private groups of investors. SoftBank Chief Operating Officer Marcelo Claure will purchase over $500 million of T-Mobile stocks, a regulatory filing disclosed.

It total, SoftBank will sell around two-thirds of the group's 25 percent share in T-Mobile. Softbank also gave Deutsche Telekom AG, which owns 44 percent stake in T-Mobile, call options to buy its remaining T-Mobile stocks. The call options will last until 2024. T-Mobile will get $300 million as fee from Softbank for facilitating the transactions.

The Japanese corporation is seeking to stabilize a balance sheet ravaged by write downs that caused the Vision Fund's last fiscal year's historic 1.9 trillion yen ($18 billion) loss. When concerns grew over investments, Son responded in rapid succession with share repurchases, completing a $4.7 billion buyback program in just three months.

T-Mobile will hold a public offering of 133.5 million shares of its common stock as part of a complex series of transactions unveiled Tuesday, the carrier said on a statement. It will also issue 10 million shares to the underwriters. In addition, T-Mobile plans to sell up to 30 million common shares to a statutory trust in Delaware.