SoftBank Group Corp. plans to spend up to ¥500 billion ($4.8 billion) buying back as much as 7 percent of its shares, taking a step advocated by activist investor Elliott Management Corp. to boost stockholder value.

The repurchases will run from March 16 of this year through March 15, 2021, and the shares will be retired, the company said Friday. SoftBank's shares fell despite the announcement, dropping as much as 9.2 percent along with the broad market decline.

The scale however falls far short of the buyback Elliott envisioned. The activist investor disclosed a stake of almost $3 billion in SoftBank in February, arguing that the company's shares were substantially undervalued given assets including a stake in Chinese e-commerce giant Alibaba Group Holding Ltd. Elliott advocated for the repurchase of as much as $20 billion, along with governance changes and more transparency about the firm's investments.

Founder Masayoshi Son has also argued his shares are undervalued, and SoftBank itself calculates that its stock may be worth more than double the current price. But the company's portfolio of startups — which includes struggling names like WeWork and Oyo Hotels — remains particularly vulnerable to economic and market shocks from the COVID-19 pandemic. The investment giant's five-year senior credit default swaps — a hedging tool that indicates the risk of a company going under — spiked Thursday to their highest levels since 2016.

"The buyback continues SoftBank's practice of repurchases following large drops in the share price," said Justin Tang, head of Asian research at United First Partners in Singapore. "Given the long drawn-out acquisition period, it is unlikely to provide much support in the market driven by emotions."