Softbank's mobile unit is set to increase its stake in Yahoo Japan by $2bn (£1.5bn) ahead of its listing in Tokyo.
As part of a three-way transaction with US firm Altaba, the deal will see Softbank increase its stake in Yahoo Japan to 48.17 per cent.
Once the ¥ 221bn (£1.5bn) in Yahoo Japan shares have been transferred to Softbank, Yahoo Japan will then buy back ¥ 220bn in shares from Softbank.
As a result of the deal, Yahoo Japan's share price was up 11 per cent as markets closed in Asia, after falling 27 per cent over the last year.
Softbank is intending to list its domestic mobile unit on the Tokyo Stock Exchange in due course, utilising the increase in its Yahoo stake to boost its ties with the e-commerce sector.
Masayoshi Son, SoftBanks chairman and chief executive, said in a statement:
I have strong confidence in the future performance of Yahoo Japan and Im excited about the significant synergies between SoftBank and Yahoo Japan.
Softbank's own share price closed 2.1 per cent higher this morning.