The legendary US investor, known as the Oracle of Omaha, first revealed he had stakes in the trading houses, also known as shosha, in 2020. The conglomerates have benefited from his interest and have also, in recent years, sharpened their focus on shareholder returns and balancing their portfolios to cut exposure to volatile sectors like natural resources.

“We see this additional acquisition as a sign of the firm’s continued confidence and trust in our company, and we will further strengthen our business portfolio,” a Mitsui spokesperson said in an email. Berkshire’s holding hasn’t exceeded 10% on a voting rights basis, it said. The US company held 9.82% of Mitsui as of March, according to data compiled by Bloomberg.

Buffett’s company has holdings in Japan’s five biggest trading firms, also including Marubeni Corp., Itochu Corp. and Sumitomo Corp. The companies are very diverse, with sprawling interests ranging from overseas oil and gas to salmon farming and convenience stores.

Mitsubishi’s shares closed up 1.9% in Tokyo, while Mitsui, Itochu and Marubeni all climbed 1.2%. Sumitomo finished 1.1% higher.

“Berkshire’s continued ownership has brought renewed attention” to the trading houses, said Norikazu Shimizu, an analyst at Iwai Cosmo Securities. They are becoming “more proactive” at ramping up shareholder returns through things like share buybacks, he added.

The US company had originally planned to keep its stakes below 10%, but the Japanese firms have agreed to relax the ceiling “moderately,” according to Buffett’s annual investor letter from February.

Filings on the Federal Energy Regulatory Commission’s website show that Berkshire Hathaway had applied for approval to purchase additional stakes in the Japanese trading firms earlier in May. The FERC authorized the transactions earlier this month, according to the filings.