It refers to the practice of categorizing people into one of two groups -- insiders or outsiders. Family, friends and close acquaintances are insiders, referred to as "uchi," while "soto" is for those relegated to the periphery.
For this Japan-obsessed student in Vietnam, it felt like a warning: she could be about to enter a deeply closed society that would always consider her an outsider.
Ultimately, though, that was not Nguyen's experience. The 25-year-old discovered that Japan was slowly changing.
As Japan's population gets older and smaller, the government is struggling to balance its own deeply conservative views on immigration with the need for new and younger workers. Public opinion is on the side of change. Despite perceptions of xenophobia, a 2018 Pew survey
revealed that 59% of Japanese believed immigrants would actually make the country stronger.
This week, Japanese lawmakers approved a policy change proposed by Prime Minister Shinzo Abe that will create new visa categories to allow an estimated 340,000 foreign workers to take both high-skilled and low-wage jobs in Japan over the next five years.
While this represents a major shift in Japan's approach to immigration, many experts argue it doesn't go far enough.
Japan is already a "super-aged" nation -- meaning that more than 20% of its population is over 65 years old. Just 946,060 babies were born in 2017, a record low since official records began in 1899, while an increase in deaths accelerated the population decline.
The decline means a shrinking cohort of workers
is left supporting an increasingly elderly population in need of healthcare and pensions.