Japan has now outlawed the resale of digital game keys.
A revision of the nation's Unfair Competition Prevention Act introduced a series of amendments that affect the games industry, and in particular the modding scene.
The official information on the amendments is currently only available in Japanese, but various translations all indicated that three acts have now been banned:

  1. Distributing tools and programs for altering save data
  2. Reselling software product keys online without the creator's permission
  3. Offering services that modify save data on the customer's behalf

This all stems from the fact that the Unfair Competition Prevention Act now recognises "data (information recorded in electromagnetic record)" as a target for protection by the law.
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, up to five years in prison, or both.