The company has been one of the largest foreign investors in Australia since the 1960s, with new investment of $14 billion in the past 10 years, which has made Australia its largest offshore operation and the destination of Mr Yasunaga's first overseas trip since taking over.
In recent weeks Mitsui has pursued investment in teleshopping in India and battery storage in the United States and Mr Yasunaga said his task was to nurture this shift in emphasis away from the longstanding strength and expertise in resources.
"I dare to say I will devote more time and more resources to non-energy sector because we are better at mining and energy businesses."
He said in Australia, "We want to focus more on the agriculture sector, including woodchip and grains collection and export".
The new trade agreement with Japan provided new emphasis to invest in bigger export capacity out of Australia, although Mitsui would also be focused on exporting to faster-growing Asian countries, he said.
But he hoped to build on his previous responsibility for Mitsui's joint venture with equipment company Komatsu in Australia to beef up the supply of more remote-controlled equipment to the Australian mining sector to improve productivity.
He was confident that Japan would continue to be dependent on coal for electricity production because of uncertainty about the revival of nuclear power plants and slow development of renewable energy.
But he said Mitsui expected the US to impose strict new emission controls on power plants and "we have to deal with that by way of introducing new technology to power plants".
While the Japanese trading houses have traditionally had only small stakes in Australian resources projects, unlike many other foreign investors, Mr Yasunaga said the company's attitude to seeking greater control was changing in many of its new investments.
"We are now changing little by little and we are now taking more ownership ratio in downstream projects like chemicals in the US, where we took a majority and run the business by ourselves.
"Wherever we can take operatorship we should do that. Of course, we have to analyse risk versus return but if it makes sense we should take operatorship."