KIEV, Ukraine — Masayoshi Son is Japan’s richest man, and one of the world’s most prolific dealmakers, and for the past few months he has been looking to add another jewel to his sprawling sports portfolio: FIFA.

For months, a consortium led by SoftBank, the Japanese conglomerate owned by Son, and the leadership of soccer’s governing body have been in negotiations over a proposed $25 billion deal for two new tournaments. The talks are shrouded in nondisclosure agreements. But according to information reviewed by The New York Times this week, the terms of the proposal call for Son to play a major role in the new joint venture, FIFA Digital Corp., and for the consortium to take over some of FIFA’s most valuable operations.

According to the proposed terms, FIFA would be a 51 percent partner in the new joint venture. The consortium, which includes SoftBank’s British subsidiary SB Investment Advisers and Centricus Partners, a London-based asset management firm, as well as Arab and American investors, also is seeking to control the rights to FIFA’s gaming and merchandise businesses. That include the soccer body’s $150 million-a-year deal with EA Sports for the popular FIFA video game, which is among its most lucrative. Son and FIFA’s president, Gianni Infantino, would serve as the co-chairmen of a 10-member supervisory board of FIFA Digital, with each appointing half the board’s members.

Son’s biggest challenge, though, is that he is seeking to acquire a multibillion-dollar stake in a governing body that many executives at the top levels of soccer say should not be for sale.