As of December, a new Japanese legal amendment has made it illegal to resell digital game keys without explicit consent from software makers.
The new set of rules are part of a revision to the Unfair Competition Prevention Act, which now recognizes "data (information recorded in electromagnetic record)" as a target for protection by law.
While key reselling has been somewhat of a grey area in the industry, it looks as though this revision will have more of an impact on modders, since it specifically targets distribution of mod tools and services.
For example, Cyber Gadget’s PlayStation 4 save editor is now discontinued on the official site, although it still seems to be available through other retailers.
However, it's likely that sites that resell keys for discounts or facilitate reselling between individuals will now be affected too.
According to the translated information, punishments range from civil measures, such as claims for damages, to criminal penalties, including fines of up to ¥5 million (~$46,000 USD), up to at least five years in prison, or both.