Hirata, the 35-year-old son of Japanese migrants, said he was born in Brazil and would root for his beloved Selecao if they face off with the Blue Samurai in the tournament.
"But if Japan beat Brazil, I wouldn't be sad," said the kung fu academy manager.
Hirata and other Japanese-Brazilians do not have to worry about such a matchup for now as the two teams are not in the same group and do not risk crossing paths until at least the quarter-finals.
Brazil is home to the world's largest Japanese community outside Japan, with some 1.8 million people of Japanese descent. About 60 percent live in Sao Paulo state.
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The first wave of Japanese migrants came to Brazil to flee poverty in their country and work in the South American country's coffee plantations under an agreement between the two governments.
Sao Paulo's Japanese neighborhood is in a district called Liberdade, a neighborhood lined with red Japanese-style street lights, restaurants serving tempura and shops selling anime videos.
But when it comes to football, it remains difficult for some to choose between Brazil and the country of their elders who arrived in the first wave of Japanese migration in 1908.