Hedge fund manager Seth Fischer has a powerful ally as he campaigns for Japanese companies to sell their stakes in each others' businesses: Prime Minister Shinzo Abe.

Not that it's made much difference. Kyocera Corp. still owns a $9 billion (¥981 billion) slice of KDDI Corp., the phone company with which it shares a founder, despite Fischer pushing since at least 2015 for a sale. Electronics maker Kyocera offloaded a small part of the holding last year, but otherwise hasn't budged, and the investment makes up about 40 percent of its own market value.

"They absolutely do not have to own the stake," Fischer, the chief investment officer of Hong Kong-based Oasis Management Co., said in a phone interview. "We will continue to engage."