I worked in Japan for two years and I paid taxes and from the salary, pension was deducted as well. Since I am back to Malaysia, I wanted to claim back the money deducted for the pension earlier. So, I applied for it and got back 80% of the total amount, 20% was taken out by the Japanese government as tax. To get back the 20%, one needs to have a friend or acquaintance in Japan who is willing to go to the local tax office to settle the procedures.
*Local tax office - the tax office in the city 市 / district 区 where you paid resident tax before. So, let's say I stayed in Kumamoto Shi before and I have a friend in Hokkaido, he or she will have to go all the way south from Hokkaido to Kumamoto Shi to settle all the paperworks for me. So, unless the amount is very big, normally people will just let go of the 20%. It is just not worth the trouble.