This scheme is part of Japan's tax system. If you are not a Japanese tax resident, different carryforward rules will apply under the tax law of your own country.
How it works
If a loss from selling stocks or similar assets in a given year remains after being offset (see the Loss Offsetting page) against that year's gains, the remaining loss can be carried forward to future years and offset against future gains.
Things to watch for
To use tax loss carryforward, you are generally required to file a tax return (see related page) not only in the year the loss occurred but continuously in the following years as well. Please confirm the requirements and procedure with a qualified tax accountant.