Warren Buffett's Berkshire Hathaway has raised its stakes in Japan's five leading trading houses by at least 1 percentage point to more than 6%, regulatory filings showed on Monday. The conglomerate's stakes rose to 6.6% from 5% in Mitsubishi Corp. , to 6.6% from 5% in Mitsui & Co ., to 6.2% from 5% in Itochu Corp ., to 6.8% from 5.1% in Marubeni Corp. and to 6.6% from 5% in Sumitomo Corp ., filings showed. Buffett first acquired these stocks on his 90th birthday in August 2020 through regular purchases on the Tokyo Stock Exchange. The legendary investor previously said he intends to hold the investments for the long term, and that it may increase its holdings in any of the companies up to a maximum of 9.9%, depending on price. Marubeni and Mitsubishi shares jumped more than 2% after the news on Monday. Sumitomo and Itochu shares rose about 1%. These Japanese trading firms, also known as sogo shosha, are highly diversified companies involved in a wide range of products and services, including energy, machinery, chemicals, food, finance and banking, Itochu, Marubeni, Mitsubishi, Mitsui, and Sumitomo — widely known as the big five in Japan — have been vital to the Japanese economy and global trade since they emerged in the post-WWII period. They are essentially conglomerates just like Berkshire. These stocks have all rallied double digits this year, outperforming Japanese equity benchmark Nikkei 225 's 3% loss in 2022. Shares of Mitsui have climbed more than 40% this year, while Sumitomo and Marubeni have both risen about 30%. Mitsubishi and Itochu have jumped about 20% in 2022. The "Oracle of Omaha" has been a net buyer of stocks for four straight quarters. In a recent move, he took a $4 billion stake in Taiwan Semiconductor , sparking a big rally in the chipmaker.