The most common visa status among foreign workers in Japan is “technical intern trainee”; the trainee program was established to transfer skills and knowledge to developing countries.
The aftermath of the 2011 Great East Japan Earthquake prompted a sharp rise in Vietnamese workers in Japan. China had previously been the main supply of labor to Japan, but the country’s economic development made working in Japan less attractive, and the disaster led to the departure of Chinese nationals. Major anti-Japan demonstrations in China accelerated this trend, and Vietnam became a new source for Japan’s foreign labor needs.
“Rising prices in Japan mean increased costs, and people are saying across Vietnam that you can no longer make money there. There used to be an unspoken rule that there would be three times as many applicants as positions available, but now it’s hard to get twice as many.”
https://www.nippon.com/en/in-depth/d01054/