Effective July 1, 2015, Japan will institute an "Exit Tax" on Japanese residents. If a Japanese resident has lived in Japan for 5 of the last 10 years and then moves to another country (or gives up residence), the Exit Tax will create a deemed sale of all of such person's assets, triggering capital gains.
The purpose behind the new tax is of course to raise revenue for the Japanese government. Under the old rules, a Japanese resident could move to another country for a year, sell his or her assets, and avoid the Japanese capital gains tax because the Japanese government only had the right to impose an income tax on residents. (This is different from the US income tax which imposes an income tax on assets worldwide, subject to treaties and certain exceptions.)
There are numerous exceptions to the Japanese Exit Tax. The most important exception is that it only applies to individuals who have assets in excess of 100 million yen (approximately $820,000). Another major exception is that it does not apply to foreign expatriate employees staying in Japan on a working Visa.
KPMG has a detailed explanation of who is affected by the Exit Tax.
