Berkshire Hathaway has increased its investment in Japanese trading house Mitsui & Co., buying an additional 6.6 million shares to raise its total stake to over 10%. This move makes Warren Buffett's firm one of Mitsui's largest shareholders and signals a deepening commitment to its strategy of investing in Japan's major trading companies, known as sogo shosha. The investment comes at a time when Berkshire has been a net seller of stocks in the U.S. market for twelve consecutive quarters and has accumulated a record cash hoard of nearly $382 billion. Buffett's continued buying in Japan, particularly in a company like Mitsui which is involved in energy and supply chains, contrasts with his cautious stance on U.S. valuations.