Japanese pension, nenkin

It is mandatory to sign up for a Japanese retirement pension, nenkin.

Because Japan is a rapidly aging country, the government requires all adult residents between 20 and 59 years of age to contribute to the pension system. This includes workers, students, and working holiday makers.

There are two types of retirement contributions systems in Japan:

• Kosei nenkin, which consists of a percentage of an employee’s salary automatically being withheld. This applies only to employees on a permanent contract.
• Kokumin nenkin, which is the national pension fund that everyone contributes to.
  Unemployed individuals, such as students and WHV holders without a job, can apply for exemption from paying contributions.

If you do work and contribute, you should check whether your home country has an agreement with Japan that allows your pension contributions in Japan to be recognized upon your return.
You can also read this PDF document explaining the Japanese pension system.