TOKYO—Japan’s SoftBank Group Corp. unveiled a second technology megafund even bigger than its nearly $100 billion Vision Fund, answering skeptics who questioned whether anyone could raise so much in such a short time.

Vision Fund 2, as the company is calling it, expects to gather some $108 billion in capital from more than a dozen investors that have signed memorandums of understanding, ranging from Apple Inc. and Microsoft Corp. to Kazakhstan’s sovereign-wealth fund, SoftBank said Friday. Some $38 billion of that capital...