Armed with a sheaf of test certificates vouching for the safety of the produce following the March 2011 nuclear disaster there, the 37-year-old was in Paris to show the world what Fukushima has to offer.
"Even when they smiled the farmers were sad," he told AFP, explaining that products from the affected area had become tainted in the eyes of consumers and now sold at half the price they did before the accident.
The situation was so bad, he said, that he thought "it was all over".
Large swathes of the area were evacuated after the earthquake and tsunami two years ago that triggered the emergency at the Fukushima Daiichi nuclear power station.
The plant's reactors went into meltdown and spread radiation over a wide area.
For months afterwards, Hagi's own restaurant in the city of Iwaki, around 30 kilometres (18 miles) from Fukushima Daiichi, was deserted as people feared that everything in the region had been contaminated.
Many fled this key agricultural area, which now has the highest proportion of fallow land in Japan.
But Hagi opted not to join the exodus.
On the contrary, he decided that not only would he stay but he would cook with products exclusively from the region.
The publicity generated by his initiative turned around the fortunes of his own restaurant, and now the chef is determined to do what he can to help others revive their livelihoods too.
And so, over the past month, the chef found himself in the kitchens of the presidential Elysee Palace in Paris and the royal residence of Prince Albert in Monaco.
Invited to Europe by the Club des Chefs des Chefs -- whose elite membership is made up of the current personal chefs of heads of state -- Hagi spent two weeks at the Elysee followed by a stint in Monaco.
He met both President Francois Hollande and Prince Albert, in their cases serving up Japanese menus using European produce.
In Paris, he also cooked with chef Thierry Marx at Sur Mesure, his restaurant at the Mandarin Oriental Hotel which holds two Michelin stars.
The chef speaks with pride of Fukushima "baby peaches, tiny and sweet" and the smoked chicken from the region that he brought with him.
"I was very moved to come to France with this chicken," he said, adding that Paris is important as one of the gastronomic capitals of the world.
Gilles Bragard, of the Club des Chefs des Chefs said the visit would help lift the spirits of restaurateurs and farmers in Fukushima.
Even though most of the large Fukushima area was unaffected by the disaster, prices for produce have plunged and consumers continue to avoid food carrying the Fukushima tag.
"If the French eat these products, the Japanese can regain confidence and buy them again," Bragard said.
The chef, who has just returned home to Japan, was an "ambassador for the products of Fukushima... It has become his crusade," he added.
The visit also served as a welcome boost for Hagi's own morale.
"All these chefs gave me the courage to continue. I feel reinvigorated," he said.
"We must motivate people to continue reconstructing Fukushima," he said.