Warren Buffett turned 90 years old yesterday, and he made sure everyone knew he's still going strong. His company Berkshire Hathaway (BRK.A -1.63%) (BRK.B -1.66%) announced that over the past approximately 12 months, it has accumulated stakes in five of the leading Japanese trading companies of slightly more than 5% each. At today's share prices, the total investment is valued at about $6.25 billion. 

The Japanese firms are Itochu (ITOCF), Marubeni (MARUY -1.93%), Mitsubishi (MBFJ.F 1.33%)Mitsui (MITSY -0.26%) and Sumitomo (CMTD.F 2.45%). Berkshire bought the shares through normal open purchases on the Tokyo stock exchange. 

warren buffett profile picture from 2015

Image source: The Motley Fool.

Buffett has been known for his long-term investments. Recently, however, his company has announced some notable sales, including all of its airline stocks and 25% of its long-held Wells Fargo (WFC -0.02%) stake. 

Berkshire said its intention is to hold the Japanese trading companies for the long term. It also said these investments are passive, and Berkshire will not raise its ownership stakes in any of the five firms to more than 9.9% "unless given specific approval by the investee's board of directors."

Buffett commented, "I am delighted to have Berkshire Hathaway participate in the future of Japan," while also noting that the trading companies have joint ventures around the world that he believes are likely to increase. He added, "I hope that in the future there may be opportunities of mutual benefit."

The five Japanese companies deal in materials including metals, textiles, food and energy. Berkshire Hathaway's collection of companies include some in these fields and may be a source for mutually beneficial work in the future.