The number of Vietnamese in Japan surged 31.2% in the past year.

Hard Work, Low Payment Push Many Vietnamese in Japan into Illegitimate Residence Status
Vietnamese people in Tokyo, Japan, gather together to make traditional cakes for Tet, or Lunar New Year in February 2018. Photo by VnExpress/Hoang Son Lam
In March this year, Japan Times cited the data from the Japanese Justice Ministry that The number of foreign nationals who lived in Japan as of the end of 2017 grew 7.5 percent from a year earlier to hit a record high of 2,561,848, reflecting a jump in Vietnamese residents.
Also according to the Japanese Justice Ministry, in Japan, the number of Chinese increased 7,5% from the previous year to 730.890, accounting for 28.5% of the total. 
Among the legal residents, those from China increased 7.5 percent from the previous year to 730,890, accounting for 28.5 percent of the total. South Koreans came second at 450.663, the Vietnamese ranked third at 262.405, up 31.2%.
Since 2013 when then Japan really started to become one of the most favorite destination for Vietnamese studing overseas and labor exporting, the number of Vietnamese in Vietnam has surged more than 5 times. 
Howevers, the surge of Vietnamese in Japan comes at a cost. The Japanese Justice Ministry also said that the number of residents whose visa status was illegitimate as of Jan.1 this year rose 1.9% to 66.498, up for the fourth consecutive year. This uprising was attributed to the surge of people in Vietnam.
There are many reasons behind the number of Vietnamese with illegitimate visa status in Japan. Before coming to Japan, many of them had been cheated by the middlemen about the high earning prospects in Japan; thus they heavily borrowed money from banks or relatives to have money to go to Japan.
Later when they came to Japan, they faced with the bitter reality of low earning manual jobs, continual night shifts and the strict restriction in terms of number of allowed working hours. Many of them can not earn back the money borrowed even until the working term finished, then they found the way to escape to earn more money with the hope to cover heavy loads of debts.