## 1 Introduction  
In Japan, a rapid aging of population and the decreasing fertility rate have been recognized as a big issue in social sustainability. To solve these problems, increasing the fertility rate and accepting foreign migrants are the main approaches to improve the demographic structure and national economic growth. However, the former requires a long time for substantial increase or supplying labor force to the industries, so that it is not appropriate for an immediate countermeasure. Therefore, the latter is a possible solution, as it is more quick and effective in resolving the need of Japan's workforce and social problems. Even though international migration to Japan is smaller than that of other industrialized countries in Europe and North America, foreign people have been a source of labor force supply in various industries in Japan. The industries suffering from a labor force shortage are agriculture, food-processing, and construction sectors. For those industries, the foreign workforce is an important stabilizer of labor supply in the current aging society of Japan. The number of migrants has gradually increased over the last decade, so then, the social structure of foreign residents has significantly transformed and affected Japanese society [1]. Japan's foreign population has annually increased by about 200,000, while the overall Japanese population has been declining by roughly 500,000 in a year, according to the resident registration data of the Ministry of Internal Affairs and Communications (MIAC) [2]. In 2020, approximately 2.88 million foreign residents with foreign nationality were registered in Japan, which is a share of 2.2 percent of the total population in the Census of 2020, an increase of 835 thousand (43.6%) from 2015. According to the Japan Immigration Bureau (2021), China has the largest share of foreign nationals living in Japan, with 667 thousand people (27.8% of the total of the foreign residents), followed by Korea with 375 thousand (15.6%), and Vietnam with 321 thousand (13.4%). In terms of the status of foreign residents, permanent residents are 29.0%, technical intern trainees are 12.5% and students are 8.1%. There were several significant policies for foreign migrants in Japan, such as creation of Technical Intern Training Program (TITP) to solve the labor force shortage and integration of College Student and Pre-College Student status in 2010, introduction of new residency management in 2012, implementation of Technical Intern Training Act in 2017, and establishment of Specified Skilled Worker System in 2019 (Figure 1). International migration to Japan started to increase with the introduction of new residency management in 2012. Foreign workforce immigration has significantly increased after 2015 with the impact of the Japan Revitalization Strategy approved in June 2014, which includes \"Utilization of Foreign Workers\" under the \"Employment System Reform/Strengthening of Human Resources.\" Under TITP, workers from foreign countries were recruited as interns for approximately one to five years, and they were not permitted to change jobs during their stay. In keeping with the no-immigration policy in Japan, the government has provided a minimum of support to the foreign workers during their stay, and the workers were expected to return home at the end of their internship in TITP [3]. This leads to the illegal disappearance of the interns from their assigned sites when the intern has an economic need to work in Japan beyond their authorized period of stay [4]. In order to mitigate the system faults of TITP, Japanese government tried to reform the immigration scheme with a legal framework for the admission of foreign unskilled or semi-skilled workers under TITP.